Combination of searches for anomalous top quark couplings with 5.4 fb−1 of pp¯ collisions

We present measurements of the tWb coupling form factors using information from electroweak single top quark production and from the helicity of W bosons from top quark decays in t (t) over bar events. We set upper limits on anomalous tWb coupling form factors using data collected with the DO detector at the Tevatron p (p) over bar collider corresponding to an integrated luminosity of 5.4 fb(-1).

Search for a Fermiophobic and Standard Model Higgs Boson in Diphoton Final States

Made available in DSpace on 2022-04-29T01:13:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-10-05 National Science Foundation We present a search for the standard model Higgs boson and a fermiophobic Higgs boson in the diphoton final states based on 8.2fb-1 of pp̄ collisions at √s=1.96TeV collected with the D0 detector at the Fermilab Tevatron Collider. No excess of data above background predictions is observed and upper limits at the 95% C.L. on the cross section multiplied by the branching fraction are set which are the most restrictive to date. A fermiophobic Higgs boson with a mass below 112.9 GeV is excluded at the 95% C.L. © 2011 American Physical Society. Universidad de Bu…

Observation of the Doubly StrangebBaryonΩb−

We report the observation of the doubly strange b baryon Omega(-)(b) in the decay channel Omega(-)(b) -> J/psi Omega(-), with J/psi -> mu(+)mu(-) and Omega(-) -> Lambda K- -> (p pi(-))K-, in p (p) over bar collisions at root s = 1.96 TeV. Using approximately 1.3 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron Collider, we observe 17.8 +/- 4.9(stat) +/- 0.8(syst) Omega(-)(b) signal events at a mass of 6.165 +/- 0.010(stat) +/- 0.013(syst) GeV. The significance of the observed signal is 5.4 sigma, corresponding to a probability of 6.7 x 10(-8) of it arising from a background fluctuation.

Search forZZandZγ*Production inpp¯Collisions ats=1.96  TeVand Limits on AnomalousZZZandZZγ*Couplings

We present a study of mu mu mu mu, eeee, and mu mu ee events using 1 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron p (p) over bar Collider at root s = 1.96 TeV. Requiring t ...

Search for the Higgs Boson inH→WW(*)Decays inpp¯Collisions ats=1.96  TeV

We present a search for the standard model Higgs boson in H --> WW(*) decays with e+e-, e+/-mu-/+, and mu+mu- final states in pp collisions at a center-of-mass energy of square root of s = 1.96 TeV. The data, collected from April 2002 to June 2004 with the D0 detector, correspond to an integrated luminosity of 300-325 pb(-1), depending on the final state. The number of events observed is consistent with the expectation from backgrounds. Limits from the combination of all three channels on the Higgs boson production cross section times branching ratio sigma x BR(H --> WW(*) are presented.

Combined Tevatron upper limit ongg→H→W+W−and constraints on the Higgs boson mass in fourth-generation fermion models

We combine results from searches by the CDF and D0 collaborations for a standard model Higgs boson (H) in the process gg -> H -> W+W- in p (p) over bar collisions at the Fermilab Tevatron Collider at root s = 1.96 TeV. With 4.8 fb(-1) of integrated luminosity analyzed at CDF and 5.4 fb(-1) at D0, the 95% confidence level upper limit on sigma(gg -> H) x B(H -> W+W-) is 1.75 pb at m(H) = 120 GeV, 0.38 pb at m(H) = 165 GeV, and 0.83 pb at m(H) = 200 GeV. Assuming the presence of a fourth sequential generation of fermions with large masses, we exclude at the 95% confidence level a standard-model-like Higgs boson with a mass between 131 and 204 GeV.

Measurement of the Effective Weak Mixing Angle inpp¯→Z/γ*→e+e−Events

We present a measurement of the fundamental parameter of the standard model, the weak mixing angle, in $p\bar{p}\rightarrow Z/\gamma^{*}\rightarrow e^{+}e^{-}$ events at a center of mass energy of 1.96 TeV, using data corresponding to 9.7 fb$^{-1}$ of integrated luminosity collected by the D0 detector at the Fermilab Tevatron. The effective weak mixing angle is extracted from the forward-backward charge asymmetry as a function of the invariant mass around the Z boson pole. The measured value of $\sin^2\theta_{\text{eff}}^{\text{$\ell$}}=0.23146 \pm 0.00047$ is the most precise measurement from light quark interactions to date, with a precision close to the best LEP and SLD results.

Search for the Standard Model Higgs Boson in theZH→νν¯bb¯Channel in5.2  fb−1ofpp¯Collisions ats=1.96  TeV

A search is performed for the standard model Higgs boson in 5.2 fb-1 of p-pbar collisions at sqrt(s)=1.96 TeV, collected with the D0 detector at the Fermilab Tevatron Collider. The final state considered is a pair of b jets and large missing transverse energy, as expected from p-pbar->ZH->vvbb production. The search is also sensitive to the WH->lvbb channel when the charged lepton is not identified. For a Higgs boson mass of 115 GeV, a limit is set at the 95% C.L. on the cross section multiplied by branching fraction for p-pbar->(Z/W)H and H->bb that is a factor of 3.7 larger than the standard model value, consistent with the factor of 4.6 expected.

Search for the standard model Higgs boson in the ZH→νν¯bb¯ channel in 9.5 fb−1 of pp¯ collisions at s=1.96 TeV

We present a search for the standard model Higgs boson in 9.5 fb-1 of ppbar collisions at sqrt(s) = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The final state considered contains a pair of b jets and is characterized by an imbalance in transverse energy, as expected from ppbar->ZH->vvbb production. The search is also sensitive to the WH->lvbb channel when the charged lepton is not identified. The data are found to be in good agreement with the expected background. For a Higgs boson mass of 125 GeV, we set a limit at the 95% C.L. on the cross section sigma(ppbar->[Z/W]H), assuming standard model branching fractions, that is a factor of 4.3 times larger than th…

Energy-energy correlations in hadronic final states from Z0 decays

We have studied the energy-energy angular correlations in hadronic final states from Z0 decay using the DELPHI detector at LEP. From a comparison with Monte Carlo calculations based on the exact second order QCD matrix element and string fragmentation we find that Λ(5)/MS = 104-20 +25 (stat.)-20 +25(syst.)-00 +30(theor.) MeV, which corresponds to αs(91 GeV) = 0.106± 0.003 (stat.)±0.003(syst.)-0.000 +0.003(theor.). The theoretical error stems from different choices for the renormalization scale of αs. In the Monte Carlo simulation the scale of αs as well as the fragmentation parameters have been optimized to described reasonably well all aspects of multihadron production.

Identified particles in quark and gluon jets

A sample of about 1.4 million hadronic Z decays, selected among the data recorded by the DELPHI detector at LEP during 1994, was used to measure for the first time the momentum spectra of K+, K-0, p, Lambda and their antiparticles in gluon and quark jets. As observed for inclusive charged particles, the production spectra of identified particles were found to be softer in gluon jets than in quark jets, with a higher total multiplicity. (C) 1997 Published by Elsevier Science B.V.

Measurement of directCPviolation parameters inB±→J/ψK±andB±→J/ψπ±decays with10.4  fb−1of Tevatron data

We present a measurement of the direct CP-violating charge asymmetry in B-+/- mesons decaying to J/psi K-+/- and J/psi pi(+/-) where J/psi decays to mu(+)mu(-), using the full run II data set of 10.4 fb(-1) of proton-antiproton collisions collected using the D0 detector at the Fermilab Tevatron Collider. A difference in the yield of B- and B+ mesons in these decays is found by fitting to the difference between their reconstructed invariant mass distributions resulting in asymmetries of A(J/psi K) = [0.59 +/- 0.37]%, which is the most precise measurement to date, and A(J/psi pi) = [-4.2 +/- 4.5]%. Both measurements are consistent with standard model predictions.

Measurement of theϕη*distribution of muon pairs with masses between 30 and 500 GeV in10.4  fb−1ofpp¯collisions

We present a measurement of the distribution of the variable phi(eta)* for muon pairs with masses between 30 and 500 GeV, using the complete run II data set collected by the D0 detector at the Fermilab Tevatron proton-antiproton collider. This corresponds to an integrated luminosity of 10.4 fb(-1) at root s = 1.96 TeV. The data are corrected for detector effects and presented in bins of dimuon rapidity and mass. The variable phi(eta)* probes the same physical effects as the Z/gamma* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. These are the first measurements at any collider of the phi(eta)* distributions for dilepton masses aw…

Search forWHassociated production inpp¯collisions ats=1.96  TeV

This report describes a search for associated production of W and Higgs bosons based on data corresponding to an integrated luminosity of L approximate to 5.3 fb(-1) collected with the D0 detector at the Fermilab Tevatron p (p) over bar Collider. Events containing a W -> l nu candidate (with l corresponding to e or mu) are selected in association with two or three reconstructed jets. One or two of the jets are required to be consistent with having evolved from a b quark. A multivariate discriminant technique is used to improve the separation of signal and backgrounds. Expected and observed upper limits are obtained for the product of the WH production cross section and branching ratios and …

Search for Z0 decays to two leptons and a charged particle-antiparticle pair

Based on a sample equivalent to 365 000 hadronic Z0 decays, the search in DELPHI data for pairs of leptons accompanied by a pair of charged particles is described. A total of 11 events were found in the electron channel, 9 in the muon channel and 7 in the tau channel. Results on lepton pairs with a radiated photon are also presented. The data from all channels are compatible with the expectations from standard processes. However, one event was found in the tau channel with an unusually high mass of the charged particle pair.

Updated precision measurement of the average lifetime of B hadrons

The measurement of the average lifetime of B hadrons using inclusively reconstructed secondary vertices has been updated using both an improved processing of previous data and additional statistics from new data. This has reduced the statistical and systematic uncertainties and gives \tau_{\mathrm{B}} = 1.582 \pm 0.011\ \mathrm{(stat.)} \pm 0.027\ \mathrm{(syst.)}\ \mathrm{ps.} Combining this result with the previous result based on charged particle impact parameter distributions yields \tau_{\mathrm{B}} = 1.575 \pm 0.010\ \mathrm{(stat.)} \pm 0.026\ \mathrm{(syst.)}\ \mathrm{ps.}

Search for Randall-Sundrum Gravitons in the Dielectron and Diphoton Final States with5.4  fb−1of Data frompp¯Collisions ats=1.96  TeV

Using 5.4 fb-1 of integrated luminosity from ppbar collisions at sqrt(s)=1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider, we search for decays of the lightest Kaluza-Klein mode of the graviton in the Randall-Sundrum model to ee and gammagamma. We set 95% C.L. lower limits on the mass of the lightest graviton between 560 GeV and 1050 GeV for values of the coupling k/Mbar_pl between 0.01 and 0.1.

Search for admixture of scalar top quarks in the tt¯ lepton + jets final state at s=1.96 TeV

A search for pair production of the lightest supersymmetric partner of the top quark is performed in the lepton+jets channel using 0.9 fb-1 of data collected by the D0 experiment. Kinematic differences between scalar top quark pair production and the dominant top quark pair production background are used to separate the two processes. First limits from Run II of the Fermilab Tevatron Collider for the scalar top quark decaying to a chargino and a b quark are obtained for scalar top quark masses of 130-190 GeV and chargino masses of 90-150 GeV.

Search for Third-Generation Scalar Leptoquarks inpp¯Collisions ats=1.96  TeV

We report on a search for charge-1/3 third-generation leptoquarks (LQ) produced in p (p) over bar collisions at root s =1.96 TeV using the D0 detector at Fermilab. Third-generation leptoquarks are assumed to be produced in pairs and to decay to a tau neutrino and a b quark with branching fraction B. We place upper limits on sigma(p (p) over bar -> LQ (LQ) over bar )B-2 as a function of the leptoquark mass M-LQ. Assuming B=1, we exclude at the 95% confidence level third-generation scalar leptoquarks with M-LQ < 229 GeV.

Measurement of theWZandZZproduction cross sections using leptonic final states in8.6  fb−1ofpp¯collisions

We study the processes p (p) over bar -> WZ -> l(+) vl(+) l(-) and p (p) over bar -> ZZ -> l(+) l(-) v (v) over bar, where l = e or mu. Using 8: 6 fb(-1) of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron collider, we measure the WZ production cross section to be 4.50(-0.66)(+0.63) pb which is consistent with, but slightly larger than, the prediction of the standard model. The ZZ cross section is measured to be 1: 64 +/- 0: 46 pb, in agreement with a prediction of the standard model. Combination with an earlier analysis of the ZZ -> l(+) l(-) l(+) l(-) channel yields a ZZ cross section of 1.44(-0.34)(+0.35) pb.

Measurement of three-jet differential cross sections dσ3jet/dM3jet in pp¯ collisions at s=1.96 TeV

We present the first measurement of the inclusive three-jet differential cross section as a function of the invariant mass of the three jets with the largest transverse momenta in an event in p anti-p collisions at sqrt(s) = 1.96 TeV. The measurement is made in different rapidity regions and for different jet transverse momentum requirements and is based on a data set corresponding to an integrated luminosity of 0.7 fb^{-1} collected with the D0 detector at the Fermilab Tevatron Collider. The results are used to test the three-jet matrix elements in perturbative QCD calculations at next-to-leading order in the strong coupling constant. The data allow discrimination between parametrizations …

Production of strange particles in the hadronic decays of the Z0

Abstract An analysis of the production of strange particles from the decays of the Z 0 boson into multihadronic final states is presented. The analysis is based on about 90 000 selected hadronic Z 0 decays collected by the DELPHI detector at LEP in 1990. K s 0 , K ∗± , Λ( Λ ) and Ξ − ( Ξ + ) have been identified by their characteristic decays. The measured production cross sections are compared with predictions of the Lund Monte Carlo tuned to data at PEP/PETRA energies.

Measurement of the directCP-violating parameterACPin the decayD+→K−π+π+

We measure the direct CP-violating parameter A_CP for the decay of the charged charm meson, D+ -> K-pi+pi+ (and charge conjugate), using the full 10.4 fb-1 sample of ppbar collisions at sqrt(s) = 1.96 TeV collected by the D0 detector at the Fermilab Tevatron collider. We extract the raw reconstructed charge asymmetry by fitting the invariant mass distributions for the sum and difference of charge-specific samples. This quantity is then corrected for detector-related asymmetries using data-driven methods and for possible physics asymmetries (from B -> D processes) using input from Monte Carlo simulation. We measure A_CP = [-0.16 +- 0.15 (stat.) +- 0.09 (syst.)]%, which is consistent with zer…

Measurement of theΛb0Lifetime in the DecayΛb0→J/ψΛ0with the D0 Detector

We present measurements of the Lambda(b)(0) lifetime in the exclusive decay channel Lambda(b)(0)-> J/psi Lambda(0), with J/psi ->mu(+)mu(-) and Lambda(0)-> p pi(-), the B-0 lifetime in the decay B-0-> J/psi K-S(0) with J/psi ->mu(+)mu(-) and K-S(0)->pi(+)pi(-), and the ratio of these lifetimes. The analysis is based on approximately 250 pb(-1) of data recorded with the D0 detector in p (p) over bar collisions at root s = 1.96 TeV. The Lambda(b)(0) lifetime is determined to be tau(Lambda(b)(0))=1.22(-0.18)(+0.22)(stat)+/- 0.04(syst) ps, the B-0 lifetime tau(B-0)=1.40(-) (+0.11)(0.10)(stat)+/- 0.03(syst) ps, and the ratio tau(Lambda(b)(0))/tau(B-0)=0.87(-) (+0.17)(0.14)(stat)+/- 0.03(syst). I…

Measurement of the forward-backward asymmetry in the distribution of leptons intt¯events in thelepton+jetschannel

We present measurements of the forward-backward asymmetry in the angular distribution of leptons from decays of top quarks and antiquarks produced in proton-antiproton collisions. We consider the final state containing a lepton and at least three jets. The entire sample of data collected by the D0 experiment during Run II of the Fermilab Tevatron Collider, corresponding to 9.7 inverse fb of integrated luminosity, is used. The asymmetry measured for reconstructed leptons is $A_{FB}^l = \big(2.9 \pm 2.1(stat.) ^{+1.5}_{-1.7}(syst.) \big)$%. When corrected for efficiency and resolution effects within the lepton rapidity coverage of $|y_l|<1.5$, the asymmetry is found to be $A_{FB}^l = \big(4.2…

Measurement of the Top Quark Mass Using the Matrix Element Technique in Dilepton Final States

We present a measurement of the top quark mass in ppbar collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. The data were collected by the D0 experiment corresponding to an integrated luminosity of 9.7 fb-1. The matrix element technique is applied to ttbar events in the final state containing leptons (electrons or muons) with high transverse momenta and at least two jets. The calibration of the jet energy scale determined in the lepton + jets final state of ttbar decays is applied to jet energies. This correction provides a substantial reduction in systematic uncertainties. We obtain a top quark mass of mt = 173.93 +- 1.84 GeV.

Search for neutral heavy leptons produced in Z decays

Weak isosinglet Neutral Heavy Leptons ($\nu_m$) have been searched for using data collected by the DELPHI detector corresponding to $3.3\times 10^{6}$ hadronic~Z$^{0}$ decays at LEP1. Four separate searches have been performed, for short-lived $\nu_m$ production giving monojet or acollinear jet topologies, and for long-lived $\nu_m$ giving detectable secondary vertices or calorimeter clusters. No indication of the existence of these particles has been found, leading to an upper limit for the branching ratio $BR($Z$^0\rightarrow \nu_m \overline{\nu})$ of about $1.3\times10^{-6}$ at 95\% confidence level for $\nu_m$ masses between 3.5 and 50 GeV/$c^2$. Outside this range the limit weakens rap…

Measurement of the forward-backward asymmetry of e(+)e(-)-]z-]b(b)over-bar using prompt leptons and a lifetime tag

The forward-backward asymmetry of the process e+e-→Z→b {Mathematical expression} has been measured using events collected by the DELPHI experiment during the 1991 and 1992 LEP runs. This data sample corresponded to 884 000 hadronic Z decays at a centre-of-mass energy {Mathematical expression}. The tagging of b-quark events was performed using two approaches; the first was based on the semileptonic decay channels b→X+μ and b→X+e, the second used a lifetime tag with jet-charge reconstruction. The results of these two methods were combined to give {Mathematical expression} With the semileptonic sample, the forward-backward asymmetry of the process e+e-→Z→ {Mathematical expression} was also mea…

Search for the Production of Single Sleptons throughR-Parity Violation inpp¯Collisions ats=1.8  TeV

We report the first search for supersymmetric particles via s-channel production and decay of smuons or muon sneutrinos at hadronic colliders. The data for the two-muon and two-jets final states were collected by the D0 experiment and correspond to an integrated luminosity of 94+/-5 pb(-1). Assuming that R parity is violated via the single coupling lambda(211)('), the number of candidate events is in agreement with expectation from the standard model. Exclusion contours are given in the (m(0),m(1/2)) and (m((χ) over bar),m((ν) over bar)) planes for lambda(211)(')=0.09, 0.08, and 0.07.

Search for associated Higgs boson production using like charge dilepton events inpp¯collisions ats=1.96  TeV

We present a search for associated Higgs boson production in the process p (p) over bar -> W/ZH -> l(+/-)l'(+/-) + X in ee, e mu, and mu mu final states. The search is based on data collected by the D0 experiment at the Fermilab Tevatron Collider at root s = 1.96 TeV corresponding to 5.3 fb(-1) of integrated luminosity. We require two isolated leptons (electrons or muons) with the same electric charge and additional kinematic requirements. No significant excess above background is observed, and we set 95% C. L. observed (expected) upper limits on ratio of the production cross section to the standard model prediction of 6.4 (7.3) for a Higgs boson mass of 165 GeV and 13.5 (19.8) for a mass o…

Search for the rare decayBs0→ϕμ+μ−with the D0 detector

We present a search for the flavor-changing neutral current decay B-s(0)->phi mu(+)mu(-) using about 0.45 fb(-1) of data collected in p (p) over bar collisions at root s=1.96 TeV with the D0 detector at the Fermilab Tevatron Collider. We find an upper limit on the branching ratio of this decay normalized to B-s(0)-> J/psi phi of B(B-s(0)->phi mu(+)mu(-))/B(B-s(0)-> J/psi phi) J/psi phi, the limit corresponds to B(B-s(0)->phi mu(+)mu(-))< 4.1x10(-6) at the 95% C.L., the most stringent upper bound to date.

Search for Pair Production of Scalar Bottom Quarks inpp¯Collisions ats=1.96  TeV

A search for direct production of scalar bottom quarks ((b) over bar) is performed with 310 pb(-1) of data collected by the D0 experiment in p (p) over bar collisions at root s = 1.96 TeV at the Fermilab Tevatron Collider. The topology analyzed consists of two b jets and an imbalance in transverse momentum due to undetected neutralinos (chi(0)(1)), with chi(0)(1) assumed to be the lightest supersymmetric particle. We find the data consistent with standard model expectations, and set a 95% C.L. exclusion domain in the (m(b), m(chi 1)(0)) mass plane, improving significantly upon the results from run I of the Tevatron.

Search for Neutral Higgs Bosons at Hightanβin theb(h/H/A)→bτ+τ−Channel

The first search in p (p) over bar collisions at root s = 1.96 TeV for the production of neutral Higgs bosons in association with bottom quarks and decaying in two tau leptons is presented. The cross section for this process is enhanced in many extensions of the standard model, such as its minimal supersymmetric extension (MSSM) at large tan beta. The data, corresponding to an integrated luminosity of 328 pb(-1), were collected with the D0 detector at the Fermilab Tevatron Collider. An upper limit is set on the production cross section of neutral Higgs bosons in the mass range of 90 to 150 GeV, and this limit is used to exclude part of the MSSM parameter space.

Study ofCP-violating charge asymmetries of single muons and like-sign dimuons inpp¯collisions

We measure the inclusive single muon charge asymmetry and the like-sign dimuon charge asymmetry in $p \bar{p}$ collisions using the full data set of 10.4 fb$^{-1}$ collected with the D0 detector at the Fermilab Tevatron. The standard model predictions of the charge asymmetries induced by CP violation are small in magnitude compared to the current experimental precision, so non-zero measurements could indicate new sources of CP violation. The measurements differ from the standard model predictions of CP violation in these asymmetries with a significance of 3.6 standard deviations. These results are interpreted in a framework of $B$ meson mixing within the CKM formalism to measure the relativ…

Search for right-handed W bosons in top quark decay

We present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of $t\bar{t}$ events in the lepton+jets decay mode. These data correspond to an integrated luminosity of 230pb^-1, collected by the DO detector at the Fermilab Tevatron $p\bar{p}$ Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the kinematics of the $t\bar{t}$ and decay products, which allows for the measurement of the leptonic decay angle $\theta^*$ for each event. By comparing the $\cos\theta^*$ distribution from the data with those for the expected background and signal for various values of f+, we find f+=0.00+-0.13(stat)+-0.07(syst). This …

Measurement of the lifetime of tau-lepton

The tau lepton lifetime is measured with the L3 detector at LEP using the complete data taken at centre-of-mass energies around the Z pole resulting in tau_tau = 293.2 +/- 2.0 (stat) +/- 1.5 (syst) fs. The comparison of this result with the muon lifetime supports lepton universality of the weak charged current at the level of six per mille. Assuming lepton universality, the value of the strong coupling constant, alpha_s is found to be alpha_s(m_tau^2) = 0.319 +/- 0.015(exp.) +/- 0.014 (theory). The tau lepton lifetime is measured with the L3 detector at LEP using the complete data taken at centre-of-mass energies around the Z pole resulting in τ τ =293.2 ± 2.0 (stat) ± 1.5 (syst) fs . The c…

Measurement of the W+b-jet and W+c-jet differential production cross sections in pp¯ collisions at s=1.96 TeV

We present a measurement of the cross sections for the associated production of a $W$ boson with at least one heavy quark jet, $b$ or $c$, in proton-antiproton collisions. Data corresponding to an integrated luminosity of 8.7 fb$^{-1}$ recorded with the D0 detector at the Fermilab Tevatron \ppbar Collider at $\sqrt{s}=1.96$ TeV are used to measure the cross sections differentially as a function of the jet transverse momenta in the range 20 to 150 GeV. These results are compared to calculations of perturbative QCD theory as well as predictions from Monte Carlo generators.

Study of the DecayBs0→Ds(*)Ds(*)

We report a study of the decay B-s(0)->(DsDs(*))-D-(*) using a data sample corresponding to 1.3 fb(-1) of integrated luminosity collected by the D0 experiment in 2002-2006 during run II of the F ...

Measurement of the asymmetry in angular distributions of leptons produced in dileptontt¯final states inpp¯collisions ats=1.96  TeV

We present measurements of asymmetries in angular distributions of leptons produced in t (t) over bar events in proton-antiproton collisions at the Fermilab Tevatron Collider. We consider final states where the W-+/- bosons from top quark and antiquark decays both decay into l nu (l = e, mu) resulting in oppositely charged dilepton final states with accompanying jets. Using 9.7 fb(-1) of integrated luminosity collected with the D0 detector, we find the asymmetries in lepton pseudorapidity compatible with predictions based on the standard model.

Search for Higgs boson production in trilepton and like-charge electron-muon final states with the D0 detector

We present a search for Higgs bosons in multilepton final states in pp-bar collisions at sqrt(s)=1.96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider, using the full Run II data set with integrated luminosities of up to 9.7 fb-1. The multilepton states considered are two electron plus muon, electron with two muons, muon with two hadronic tau leptons, and like-charge electron-muon pairs. These channels directly probe the HVV (V=W,Z) coupling of the Higgs boson in production and decay. The muon with two hadronic tau lepton channel is also sensitive to H to tau lepton pair decays. Upper limits at the 95% C.L on the rate of standard model Higgs boson production are derived i…

Rapidity correlations in Lambda baryon and proton production in hadronic Z0 decays

In an analysis of multihadronic events recorded at LEP by DELPHI in the years 1992 through 1994, charged hadrons are identified using the measurement of their energy loss and their Cherenkov angle. Rapidity correlations of \La-\La, proton-proton, and \La-proton pairs are compared. The agreement with the string and cluster fragmentation models is tested. For those pairs that frame a meson in terms of rapidity the compensation of strangeness is studied. For \La{}$\overline{\mathrm{p}}$ pairs the additional correlation with respect to charged kaons is analysed.

Search for Sneutrino Production ineμFinal States in5.3  fb−1ofpp¯Collisions ats=1.96  TeV

We report the results of a search for R parity violating (RPV) interactions leading to the production of supersymmetric sneutrinos decaying into emu final states using 5.3 fb^-1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider. Having observed no evidence for production of emu resonances, we set direct bounds on the RPV couplings lambda^'_311 and lambda_312 as a function of sneutrino mass.

Measurement of spin correlation in ttbar production using a matrix element approach

correlation, assuming that the spin of the top quark is either correlated with the spin of the anti-top quark as predicted by the standard model or is uncorrelated. For the first time we use a matrix-element-based approach to study ttbar spin correlation. We use {ttbar -&gt; W+bW-bbar -&gt;l+nubl-nub} final states produced in ppbar collisions at a center of mass energy sqrt(s)=1.96 TeV, where l denotes an electron or a muon. The data correspond to an integrated luminosity of 5.4 fb-1 and were collected with the dzero detector at the Fermilab Tevatron collider. The result agrees with the standard model prediction. We exclude the hypothesis that the spins of the ttbar are uncorrelated at the …

Evidence for a Particle Produced in Association with Weak Bosons and Decaying to a Bottom-Antibottom Quark Pair in Higgs Boson Searches at the Tevatron

Aaltonen, T. et al.

Measurement of the relative branching ratio ofBs0→J/ψf0(980)toBs0→J/ψϕ

We present a measurement of the relative branching fraction, R-f0/phi, of B-s(0) -> J/psi f(0)(980), with f(0)(980) -> pi(+)pi(-), to the process B-s(0) -> J/psi phi, with phi -> K+K-. The J/psi f(0)(980) final state corresponds to a CP-odd eigenstate of B-s(0) that could be of interest in future studies of CP violation. Using 8 fb(-1) of data recorded with the D0 detector at the Fermilab Tevatron Collider, we find R-f0/phi = 0.275 +/- 0.041(stat) +/- 0.061(syst).

Measurement ofσ(pp¯→Z)·Br(Z→ττ)ats=1.96  TeV

We present a measurement of the cross section for Z production times the branching fraction to tau leptons, sigma.Br(Z ->tau(+)tau(-)), in p (p) over bar collisions at root s=1.96 TeV in the channel in which one tau decays into mu nu(mu)nu(tau), and the other into hadrons+nu(tau) or e nu(e)nu(tau). The data sample corresponds to an integrated luminosity of 226 pb(-1) collected with the D0 detector at the Fermilab Tevatron collider. The final sample contains 2008 candidate events with an estimated background of 55%. From this we obtain sigma.Br(Z ->tau(+)tau(-)) = 237 +/- 15(stat)+/- 18(sys)+/- 15(lum)pb, in agreement with the standard model prediction.

Search for the rare decayBs0→μ+μ−

Contains fulltext : 111249pub.pdf (Publisher’s version ) (Open Access) Contains fulltext : 111249.pdf (Author’s version preprint ) (Open Access)

Combination of Tevatron searches for the standard model Higgs boson in the W+W- decay mode.

11 páginas, 4 figuras, 1 tabla.-- CDF Collaboration: et al.

Measurement of trilinear gauge couplings in e(+)e(-) collisions at 161 GeV and 172 GeV

Trilinear gauge boson couplings are measured using data taken by DELPHI at 161 GeV and 172 GeV, Values for WWV couplings (V = Z,gamma) are determined from a study of the reactions e(+)e(-) --> W+W- and e(+)e(-) --> We nu, using differential distributions from the WW final state in which one W decays hadronically and the other leptonically, and total cross,section data from other channels, Limits are also derived on neutral ZV gamma couplings from an analysis of the reaction e(+)e(-) --> gamma + invisible particles. (C) 1998 Elsevier Science B.V.

Measurement of the photon+b-jet production differential cross section in pp¯ collisions at s=1.96 TeV

We present measurements of the differential cross section d sigma/dp(T)(gamma) for the inclusive production of a photon in association with a b-quark jet for photons with rapidities vertical bar y(gamma)vertical bar 15 GeV and rapidity vertical bar Y-jet vertical bar ) Collider at root s = 1.96 TeV. The measured cross sections are compared with next-to-leading order perturbative QCD calculations using different sets of parton distribution functions as well as to predictions based on the k(T)-factorization QCD approach, and those from the SHERPA and PYTHIA Monte Carlo event generators.

Measurement of theZZproduction cross section and search for the standard model Higgs boson in the four lepton final state inpp¯collisions

We present a measurement of Z boson pair production in p (p) over bar collisions at 1.96 TeV with 9.6 to 9.8 fb(-1) of D0 data. We examine the final states eeee, ee mu mu, and mu mu mu mu. Based on selected data, the measured cross section in the mass region M(Z/gamma*) > 30 GeV is sigma(p (p) over bar -> Z/gamma*Z/gamma*) = 1.26(-0.36)(+0.44)(stat)(-0.15)(+0.17) X (syst) +/- 0.08 (lumi) pb; after correcting for the expected ratio of sigma (p (p) over bar -> Z/gamma*Z/gamma*) to sigma(p (p) over bar -> ZZ), we derive a cross section for p (p) over bar -> ZZ production of 1.05(-0.30)(+0.37)(stat)(-0.12)(0.14)(syst) +/- 0.06 (lumi) pb. This result is combined with a previous result from the Z…

Search for the rare decay Bs 0→μ+μ-

We present the results of a search for the flavor changing neutral current decay B-s(0) -> mu(+)mu(-) using 6.1 fb(-1) of p (p) over bar collisions at root s = 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron Collider. The observed number of B-s(0) candidates is consistent with background expectations. The resulting upper limit on the branching fraction is B(B-s(0) -> mu(+)mu(-)) < 5.1 x 10(-8) at the 95% C.L. This limit is a factor of 2.4 better than that of the previous DO analysis and the best limit to date. Published by Elsevier B.V.

Measurement of theBs0Lifetime in the Exclusive Decay ChannelBs0→J/ψϕ

Using the exclusive decay B-s(0)-->J/psi(mu(+)mu(-))phi(K+K-), we report the most precise single measurement of the B-s(0) lifetime. The data sample corresponds to an integrated luminosity of approximately 220 pb(-1) collected with the D0 detector at the Fermilab Tevatron Collider in 2002-2004. We reconstruct 337 signal candidates, from which we extract the B-s(0) lifetime, tau(B-s(0))=1.444(-0.090)(+0.098)(stat)+/-0.020(sys) ps. We also report a measurement for the lifetime of the B-0 meson using the exclusive decay B-0-->J/psi(mu(+)mu(-))K-*0(892)(K(+)pi(-)). We reconstruct 1370 signal candidates, obtaining tau(B-0)=1.473(-0.050)(+0.052)(stat)+/-0.023(sys) ps, and the ratio of lifetimes, …

Electron and Photon Identification in the D0 Experiment

The electron and photon reconstruction and identification algorithms used by the D0 Collaboration at the Fermilab Tevatron collider are described. The determination of the electron energy scale and resolution is presented. Studies of the performance of the electron and photon reconstruction and identification are summarized.

A search for neutral higgs particles in Z$^0$ decays

Abstract The search in DELPHI data for neutral Higgs bosons is described. No candidate for the Standard Model Higgs is seen in Z0 decays to H 0 ν ν , H 0 μ + μ − or H0τ+τ− after selections that proved efficient for finding simulated H0. One remaining candidate for Z0 → H0e+e− is consistent with background. Together with our earlier studies, these results restrict the H0 mass to be above 38 GeV/c2 at the 95% confidence level. No signal is found for decays of Minimal Supersymmetric Standard Model neutral Higgs bosons to τ+τ−. Limits are obtained for their decays to produce four jets.

Measurement of Dijet Azimuthal Decorrelations at Central Rapidities inpp¯Collisions ats=1.96  TeV

Correlations in the azimuthal angle between the two largest transverse momentum jets have been measured using the D0 detector in p (p) over bar collisions at a center-of-mass energy root s=1.96 TeV. The analysis is based on an inclusive dijet event sample in the central rapidity region corresponding to an integrated luminosity of 150 pb(-1). Azimuthal correlations are stronger at larger transverse momenta. These are well described in perturbative QCD at next-to-leading order in the strong coupling constant, except at large azimuthal differences where contributions with low transverse momentum are significant.

Search for long-lived particles decaying into electron or photon pairs with the D0 detector

In this Letter we report on a search for long-lived particles that decay into final states with two electrons or photons. Such long-lived particles arise in a variety of theoretical models, like hidden valleys and supersymmetry with gauge-mediated breaking. By precisely reconstructing the direction of the electromagnetic shower we are able to probe much longer lifetimes than previously explored. We see no evidence of the existence of such long-lived particles and interpret this search as a quasi model-independent limit on their production cross section, as well as a limit on a long-lived fourth generation quark.

Search for Stopped Gluinos frompp¯Collisions ats=1.96  TeV

Long-lived, heavy particles are predicted in a number of models beyond the standard model of particle physics. We present the first direct search for such particles' decays, occurring up to 100 h after their production and not synchronized with an accelerator bunch crossing. We apply the analysis to the gluino (g), predicted in split supersymmetry, which after hadronization can become charged and lose enough momentum through ionization to come to rest in dense particle detectors. Approximately 410 pb(-1) of p (p) over bar collisions at root s = 1.96 TeV collected with the D0 detector during Run II of the Fermilab Tevatron collider are analyzed in search of such "stopped gluinos" decaying in…

Search for the Flavor-Changing Neutral Current DecayBs0→μ+μ−inpp¯Collisions ats=1.96   TeVwith the D0 Detector

We present the results of a search for the flavor-changing neutral current decay B-s(0)-->mu(+)mu(-) using a data set with integrated luminosity of 240 pb(-1) of p (p) over bar collisions at roo ...

Measurement of the ratio of differential cross sectionsσ(pp¯→Z+b jet)/σ(pp¯→Z+jet)inpp¯collisions ats=1.96  TeV

We measure the ratio of cross sections, sigma(p (p) over bar -> Z + b jet)/sigma(p (p) over bar -> Z + jet), for associated production of a Z boson with at least one jet. The ratio is also measured as a function of the Z boson transverse momentum, jet transverse momentum, jet pseudorapidity, and the azimuthal angle between the Z boson with respect to the highest p(T) b tagged jet. These measurements use data collected by the D0 experiment in Run II of Fermilab's Tevatron p (p) over bar Collider at a center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity of 9.7 fb(-1). The results are compared to predictions from next-to-leading order calculations and various Monte Car…

Evidence for an anomalous like-sign dimuon charge asymmetry

We measure the charge asymmetry $A\equiv(N^{++} - N^{--})/(N^{++} + N^{--})$ of like-sign dimuon events in 6.1~fb$^{-1}$ of $p\bar{p}$ collisions recorded with the D0 detector at a center-of-mass energy $\sqrt{s}=1.96$~TeV at the Fermilab Tevatron collider. From $A$ we extract the like-sign dimuon charge asymmetry in semileptonic $b$-hadron decays: $\aslb=-0.00957\pm0.00251\thinspace({\rm stat})\pm0.00146\thinspace({\rm sys})$. It differs by 3.2~standard deviations from the standard model prediction $\aslb({\rm SM})=(-2.3^{+0.5}_{-0.6})\times10^{-4}$, and provides first evidence of anomalous $CP$ violation in the mixing of neutral $B$ mesons.

Search for Doubly Charged Higgs Boson Pair Production inpp¯Collisions ats=1.96  TeV

We present a search for pair production of doubly charged Higgs bosons in the processes $q\overline{q}\ensuremath{\rightarrow}{H}^{++}{H}^{--}$ decaying through ${H}^{\ifmmode\pm\else\textpm\fi{}\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\tau}}^{\ifmmode\pm\else\textpm\fi{}},{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\tau}}^{\ifmmode\pm\else\textpm\fi{}},{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}$. The search is performed in $p\overline{p}$ collisions at a center-of-mass energy of $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$ using an integrated l…

Constraints on Models for the Higgs Boson with Exotic Spin and Parity inVH→Vbb¯Final States

We present constraints on models containing non-standard-model values for the spin J and parity P of the Higgs boson H in up to 9.7 fb(-1) of p (p) over bar collisions at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. These are the first studies of Higgs boson J(P) with fermions in the final state. In the ZH -> llb (b) over bar, WH -> l nu b (b) over barb, and ZH -> nu nu b (b) over bar final states, we compare the standard model (SM) Higgs boson prediction, J(P) = 0(+), with two alternative hypotheses, J(P) = 0(-) and J(P) = 2(+). We use a likelihood ratio to quantify the degree to which our data are incompatible with non-SM J(P) predictions for a range…

PRODUCTION CHARACTERISTICS OF K-0 AND LIGHT MESON RESONANCES IN HADRONIC DECAYS OF THE Z(0)

An analysis of inclusive production of K0and the meson resonances K*±(892), ρ0(770), f0(975) and f2(1270) in hadronic decays of the Z0is presented, based on about 973,000 multihadronic events collected by the DELPHI detector at LEP during 1991 and 1992. Overall multiplicities have been determined as 1.962±0.060 K0mesons, 0.712±0.067 K*±(892) and 1.21±0.15ρ0(770) per hadronic Z0decay. The average multiplicities of f0(975) for scaled momentum, xp, in the range 0.05≤xp≤0.6 and of f2(1270) for 0.05≤xp≤1.0 are 0.098±0.016 and 0.170±0.043 respectively. The f0(975) and ρ0(770)xp-spectra have similar shapes. The f2(1270)/ρ0(770) ratio increases with xp. The average multiplicities…

Hard single diffraction in p̄p collisions at s=630 and 1800 GeV

Using the D empty set detector, we have studied events produced in (p) over barp collisions that contain large forward regions with very little energy deposition ("rapidity gaps") and concurrent jet production at center-of-mass energies of roots = 630 and 1800 GeV. The fraction of events with forward or central jets associated with rapidity gaps is compared to predictions for hard diffraction. We also extract the momentum loss for scattered protons in such processes. (C) 2002 Elsevier Science B.V. All rights reserved.

Performance of the DELPHI detector

DELPHI (DEtector with Lepton, Photon and Hadron Identification) is a detector for e(+)e(-) physics, designed to provide high granularity over a 4 pi solid angle, allowing an effective particle identification, It has been operating at the LEP (Large Electron-Positron) collider at CERN since 1989. This article reviews its performance.

Measurement oftt¯production in theτ+jetstopology usingpp¯collisions ats=1.96  TeV

We present a measurement of the t (t) over bar production cross section multiplied by the branching ratio to tau lepton decaying semihadronically (tau(h)) plus jets, sigma(p (p) over bar -> t (t) over bar + X) center dot BR(t (t) over bar -> tau(h) + jets), at a center of mass energy root s = 1.96 TeV using 1 fb(-1) of integrated luminosity collected with the D0 detector. Assuming a top quark mass of 170 GeV, we measure sigma(t (t) over bar) center dot BR tau h (+ j) = 0.60(-0.22)(+0.23)(stat)(-0.14)(+0.15)(syst) +/- 0.04(lumi) pb. In addition, we extract the t (t) over bar production cross section using the t (t) over bar -> tau(h) + jets topology, with the result sigma(t (t) over bar) = 6…

A measurement of the Tau topological branching ratios

Using data collected in the DELPHI detector at LEP-1, measurements of the inclusive tau branching ratios for decay modes containing one, three, or five charged particles have been performed, giving the following results: B_1 = B(\tau^- -> (particle)^- \geq 0pi^0 \geq 0K^0 \nu_\tau(\bar{\nu})) = (85.316 +/- 0.093 +/- 0.049)%; B_3 = B(\tau^- -> 2h^-h^+ \geq 0pi^0 \geq 0K^0 \nu_\tau) = (14.569 +/- 0.093 +/- 0.048)%; B_5 = B(\tau^- -> 3h^-2h^+ \geq 0pi^0 \geq 0K^0 \nu_\tau) = (0.115 +/- 0.013 +/- 0.006)%, where h is either a charged pi or K meson. The first quoted uncertainties are statistical and the second systematic.

Search for large extra spatial dimensions in dimuon production with the D0 detector

We present the results of a search for the effects of large extra spatial dimensions in $p{\bar p}$ collisions at $\sqrt{s} =$ 1.96 TeV in events containing a pair of energetic muons. The data correspond to 246 \ipb of integrated luminosity collected by the \D0 experiment at the Fermilab Tevatron Collider. Good agreement with the expected background was found, yielding no evidence for large extra dimensions. We set 95% C.L. lower limits on the fundamental Planck scale between 0.85 TeV and 1.27 TeV within several formalisms. These are the most stringent limits achieved in the dimuon channel to date.

Measurement of theΛbLifetime in the Exclusive DecayΛb→J/ψΛ

We have measured the {lambda}{sub b} lifetime using the exclusive decay {lambda}{sub b}{yields}J/{psi}{lambda}, based on 1.2 fb{sup -1} of data collected with the D0 detector during 2002-2006. From 171 reconstructed {lambda}{sub b} decays, where the J/{psi} and {lambda} are identified via the decays J/{psi}{yields}{mu}{sup +}{mu}{sup -} and {lambda}{yields}p{pi}, we measured the {lambda}{sub b} lifetime to be {tau}({lambda}{sub b})=1.218{sub -0.115}{sup +0.130}(stat){+-}0.042(syst) ps. We also measured the B{sup 0} lifetime in the decay B{sup 0}{yields}J/{psi}({mu}{sup +}{mu}{sup -})K{sub S}{sup 0}({pi}{sup +}{pi}{sup -}) to be {tau}(B{sup 0})=1.501{sub -0.074}{sup +0.078}(stat){+-}0.050(sy…

Measurement of σ(pp¯→Z+X)Br(Z→τ+τ−) at s=1.96 TeV

We present a measurement of the cross section for Z boson production times the branching fraction to tau lepton pairs sigma(p (p) over bar -> Z + X)Br(Z -> tau(+)tau(-)) in p (p) over bar collisions at root s = 1.96 TeV. The measurement is performed in the channel in which one tau lepton decays into a muon and neutrinos. and the other tau lepton decays hadronically or into an electron and neutrinos. The data sample corresponds to an integrated luminosity of 1.0 fb(-1) collected with the DO detector at the Fermilab Tevatron Collider. The sample contains 1511 candidate events with an estimated 20% background from jets or muons misidentified as tau leptons. We obtain sigma . Br = 240 +/- 8 (st…

Measurement of the DirectCP-violating Charge Asymmetry inDs±→ϕπ±Decays

We present a measurement of the direct CP-violating charge asymmetry in Ds+ → ϕ π(±) decays where the ϕ meson decays to K(+)K(-), using the full Run II data set with an integrated luminosity of 10.4  fb-1 of proton-antiproton collisions collected using the D0 detector at the Fermilab Tevatron Collider. The normalized difference A(CP) in the yield of D(s)(+) and D(s)(-) mesons in these decays is measured by fitting the difference between their reconstructed invariant mass distributions. This results in an asymmetry of A(CP) = [-0.38 ± 0.27]%, which is the most precise measurement of this quantity to date. The result is consistent with the standard model prediction of zero CP asymmetry in thi…

Observation of orbitally excited B mesons

Experimental evidence for the existence of orbitally excited B meson states is presented in an analysis of the Bπ and B*π distribution of Q = m(B**) - m(B(*)) - m(π) using Z0decay data taken with the DELPHI detector at LEP. The mean Q-value of the decays B**→ B(*)π is measured to be 284 ± 5 (stat.) ± 15 (syst.) MeV/c2, and the Gaussian width of the signal is 79 ± 5 (stat.) ± 8 (syst.) MeV/c2. This signal can be described as a single resonance of mass m = 5732 ± 5 (stat.) ± 20 (syst.) MeV/c2and full width Γ = 145 ± 28 MeV/c2. The observed shape is also consistent with the production of several broad and narrow states as predicted by the quark model and partly observed in the D-…

A Search for Sleptons and Gauginos in Z0 Decays

Using a data sample corresponding to 10 000 hadronic Z0 decays, we have searched for the production of sleptons and gauginos in the two-prong decays of Z0. No candidate remains after straightforward selections. For neutralinos, we use selection methods developed in our previous search for neutral Higgs particles. The negative results are translated into improved mass limits and parameter constraints on the minimal supersymmetric extension of the standard model.

Ratio of Isolated Photon Cross Sections in pp¯ Collisions at √s=630 and 1800 GeV

The inclusive cross section for production of isolated photons has been measured in p (p) over bar collisions at roots = 630 GeV with the DO detector at the Fermilab Tevatron Collider. The photons span a transverse energy (E-T) range from 7-49 GeV and have pseudorapidity \eta\ s = 1800 GeV to form a ratio of the cross sections. Comparison of next-to-leading-order QCD with the measured cross section at 630 GeV and the ratio of cross sections show satisfactory agreement in most of the E-T range.

FIRST MEASUREMENT OF THE STRANGE QUARK ASYMMETRY AT THE Z(0) PEAK

A measurement of the strange quark forward-backward asymmetry at the Z0 peak was performed using 718,000 multihadronic Z0 decays collected by the DELPHI detector at LEP in 1992. The s-quark was tagged by the presence of high momentum charged kaons identified by the Ring Imaging Cherenkov detector and by Λ0;s decaying into pπ-. The s-quark purity obtained was estimated for the two hadrons to be 43%. The average s-quark asymmetry was found to be 0.131±0.035 (stat.) ±0.013 (syst.). The forward-backward asymmetry was measured for unresolved d-and s-quarks, tagged by the detection of a high energy neutron or neutral kaon in the Hadron Calorimeter. The combined d-and s-quark purity was 69% and th…

Measurement of the t-channel single top quark production cross section

The D0 collaboration reports direct evidence for electroweak production of single top quarks through the t-channel exchange of a virtual W boson. This is the first analysis to isolate an individual single top quark production channel. We select events containing an isolated electron or muon, missing transverse energy, and two, three or four jets from 2.3 fb^-1 of ppbar collisions at the Fermilab Tevatron Collider. One or two of the jets are identified as containing a b hadron. We combine three multivariate techniques optimized for the t-channel process to measure the t- and s-channel cross sections simultaneously. We measure cross sections of 3.14 +0.94 -0.80 pb for the t-channel and 1.05 +…

Precision measurement of the top-quark mass inlepton+jetsfinal states

We measure the mass of the top quark in lepton + jets final states using the full sample of p (p) over bar collision data collected by the D0 experiment in Run II of the Fermilab Tevatron Collider at root s = 1.96 TeV, corresponding to 9.7 fb(-1) of integrated luminosity. We use a matrix element technique that calculates the probabilities for each event to result from t (t) over bar production or background. The overall jet energy scale is constrained in situ by the mass of the W boson. We measure m(t) = 174.98 +/- 0.76 GeV. This constitutes the most precise single measurement of the top-quark mass.

Search for exclusive decays of the Lambda_b baryon and measurement of its mass

A search for fully reconstructed \lb beauty baryons is performed using about 3 million Z decays collected with the DELPHI detector at LEP. The analysis relies on the combined use of the accurate tracking and of the hadron identification capabilities of DELPHI. A total of four events has been found, three in the \lc\ppm channel and one in the \lc\a1m channel over a small background. The \lb beauty baryon mass is measured to be (~ 5668 \pm 16~ ({\rm stat.}) \pm 8~({\rm syst.})~)~ \mv.

An improved determination of the width of the top quark

We present an improved determination of the total width of the top quark, $\Gamma_t$, using 5.4 fb$^{-1}$ of integrated luminosity collected by the D0 Collaboration at the Tevatron $p\bar{p}$ Collider. The total width $\Gamma_t$ is extracted from the partial decay width $\Gamma(t\to Wb)$ and the branching fraction $\mathcal{B}(t\to Wb)$. $\Gamma(t\to Wb)$ is obtained from the $t$-channel single top quark production cross section and $\mathcal{B}(t\to Wb)$ is measured in $t\bar{t}$ events. For a top mass of $172.5\;\rm GeV$, the resulting width is $\Gamma_t = 2.00^{+0.47}_{-0.43}$ GeV. This translates to a top-quark lifetime of $\tau_t = (3.29^{+0.90}_{-0.63})\times10^{-25}$ s. We also extra…

Tuning and test of fragmentation models based on identified particles and precision event shape data

Event shape and charged particle inclusive distributions are measured using 750000 decays of the $Z$ to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.

Search for anomalous Wtb couplings in single top quark production

Made available in DSpace on 2022-04-28T20:46:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-11-25 Science and Technology Facilities Council In 0.9fb-1 of pp̄ collisions, the D0 Collaboration presented evidence for single top quark production in events with an isolated lepton, missing transverse momentum, and two to four jets. We examine these data to study the Lorentz structure of the Wtb coupling. The standard model predicts a left-handed vector coupling at the Wtb vertex. The most general lowest dimension, CP-conserving Lagrangian admits right-handed vector and left- or right-handed tensor couplings as well. We find that the data prefer the left-handed vector coupling and set u…

Combined D0 measurements constraining theCP-violating phase and width difference in theBs0system

We combine the D0 measurement of the width difference between the light and heavy B-s(0) mass eigenstates and of the CP-violating mixing phase determined from the time-dependent angular distributions in the B-s(0)-> J/psi phi decays along with the charge asymmetry in semileptonic decays also measured with the D0 detector. With the additional constraint from the world average of the flavor-specific B-s(0) lifetime, we obtain Delta Gamma(s)equivalent to(Gamma(L)-Gamma(H))=0.13 +/- 0.09 ps(-1) and vertical bar phi(s)vertical bar=0.70(-0.47)(+0.39) or Delta Gamma(s)=-0.13 +/- 0.09 ps(-1) and vertical bar phi(s)vertical bar=2.44(-0.39)(+0.47). The data sample corresponds to an integrated luminos…

Search for the Associated Production of abQuark and a Neutral Supersymmetric Higgs Boson that Decays intoτPairs

We report results from a search for production of a neutral Higgs boson in association with a $b$ quark. We search for Higgs decays to $\tau$ pairs with one $\tau$ subsequently decaying to a muon and the other to hadrons. The data correspond to 2.7fb$^{-1}$ of $\ppbar$ collisions recorded by the D0 detector at $\sqrt{s} = 1.96$TeV. The data are found to be consistent with background predictions. The result allows us to exclude a significant region of parameter space of the minimal supersymmetric model.

Measurement and interpretation of the $W$-pair cross-section in $e^+e^-$ interactions at 161 GeV

In 1996 LEP ran at a centre-of-mass energy of 161~GeV, just above the threshold of W-pair production. DELPHI accumulated data corresponding to an integrated luminosity of $9.93 {\mathrm{~pb^{-1}}}$, and observed 29 events that are considered as candidates for W-pair production. From these, a cross-section for the doubly resonant $e^+e^-\to\mathrm{WW}$ process of $3.67~^{+0.97}_{-0.85} \pm 0.19{\mathrm{~pb}}$ has been measured. Within the Standard Model, this cross-section corresponds to a mass of the W-boson of ${\mathrm{80.40~\pm~0.44~(stat.)~\pm~0.09~(syst.) ~\pm 0.03~(LEP)~GeV}}/c^2$. Alternatively, if $m_{\mathrm{W}}$ is held fixed at its current value determined by other experiments, t…

Measurement of the ratio of inclusive cross sectionsσ(pp¯→Z+b−quark jet)/σ(pp¯→Z+jet)ats=1.96  TeV

The ratio of the cross section for $p\bar{p}$ interactions producing a $Z$ boson and at least one $b$ quark jet to the inclusive $Z+{\rm jet}$ cross section is measured using $4.2\ {\rm fb}^{-1}$ of $p\bar{p}$ collisions collected with the \dzero\ detector at the Fermilab Tevatron collider at $\sqrt{s}=1.96$ TeV. The $Z\rightarrow\ell^+\ell^-$ candidate events with at least one $b$ jet are discriminated from $Z+$ charm and light jet(s) events by a novel technique that exploits the properties of the tracks associated to the jet. The measured ratio is $0.0193\pm0.0027$ for events having a jet with transverse momentum $\pt > 20 \GeV$ and pseudorapidity $|\eta| \leq 2.5$, which is the most prec…

Combined Search for the Standard Model Higgs Boson Decaying tobb¯Using the D0 Run II Data Set

We present the results of the combination of searches for the standard model Higgs boson produced in association with a W or Z boson and decaying into b bbar using the data sample collected with the D0 detector in p pbar collisions at sqrt{s}=1.96 TeV at the Fermilab Tevatron Collider. We derive 95% CL upper limits on the Higgs boson cross section relative to the standard model prediction in the mass range 100 GeV <= M_H <= 150 GeV, and we exclude Higgs bosons with masses smaller than 102 GeV at the 95% CL. In the mass range 120 GeV <= M_H <= 145 GeV the data exhibit an excess above the background prediction with a global significance of 1.5 standard deviations, consistent with the expectat…

Search for supersymmetry with gauge-mediated breaking in diphoton events at D0

We report the results of a search for supersymmetry (SUSY) with gauge-mediated breaking in the missing transverse energy distribution of inclusive diphoton events using 263 pb$^{-1}$ of data collected by the D0 experiment at the Fermilab Tevatron Collider in 2002--2004. No excess is observed above the background expected from standard model processes, and lower limits on the masses of the lightest neutralino and chargino of about 108 and 195 GeV, respectively, are set at the 95% confidence level. These are the most stringent limits to date for models with gauge-mediated SUSY breaking with a short-lived neutralino as the next-lightest SUSY particle.

Measurement of the ratio of inclusive cross sectionsσ(pp¯→Z+2b jets /σ(pp¯→Z+2 jets)inpp¯collisions ats=1.96  TeV

In this study, we measure the ratio of cross sections, σ(pp¯ → Z + 2 b jets)/σ(pp¯ → Z + 2 jets), for associated production of a Z boson with at least two jets with transverse momentum pjetT > 20 GeV and pseudorapidity |ηjet| < 2.5. This measurement uses data corresponding to an integrated luminosity of 9.7 fb–1 collected by the D0 experiment in Run II of Fermilab’s Tevatron pp¯ Collider at a center-of-mass energy of 1.96 TeV. The measured integrated ratio of 0.0236 ± 0.0032(stat) ± 0.0035(syst) is in agreement with predictions from next-to-leading-order perturbative QCD and the Monte Carlo event generators PYTHIA and ALPGEN.

Measurement of the differential γ+c-jet cross section and the ratio of differential γ+c and γ+b cross sections in pp¯ collisions at s=1.96 TeV

We present measurements of the differential cross section $d\sigma/dp_{T}^{\gamma}$ for the associated production of a $c$-quark jet and an isolated photon with rapidity $|y^{\gamma}| 15$ GeV. The cross section ratios $\sigma(\gamma+c)/\sigma(\gamma+b)$ as a function of $p_{T}^{\gamma}$ are also presented. The results are based on data corresponding to an integrated luminosity of 8.7 fb$^{-1}$ recorded with the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider at $\sqrt{s}=$1.96 TeV. The obtained results are compared to next-to-leading order perturbative QCD calculations using various parton distribution functions, to predictions based on the $k_{T}$-factorization approach, and to pr…

Measurements of single top quark production cross sections and|Vtb|inpp¯collisions ats=1.96  TeV

We present measurements of production cross sections of single top quarks in $\ppbar$ collisions at $\sqrt{s}=1.96\;\rm TeV$ in a data sample corresponding to an integrated luminosity of $5.4\;\rm fb^{-1}$ collected by the D0 detector at the Fermilab Tevatron Collider. We select events with an isolated electron or muon, an imbalance in transverse energy, and two, three, or four jets, with one or two of them containing a bottom hadron. We obtain an inclusive cross section of $\sigma({\ppbar}{\rargap}tb+X, tqb+X) = 3.43\pm^{0.73}_{0.74}\;\rm pb$ and use it to extract the CKM matrix element $0.79 < |V_{tb}| \leq 1$ at the 95% C.L. We also measure $\sigma({\ppbar}{\rargap}tb+X) = 0.68\pm^{0.38}…

Measurements of the tau polarisation in Z0 decays

A sample of Z0→τ+τ- events observed in the DELPHI detector at LEP in 1991 and 1992 is analysed to measure the τ polarisation in the exclusive decay channels {Mathematical expression}, {Mathematical expression}, πν, ρν and a1ν. The τ polarisation is also measured with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision than the use of the exclusive decay modes. The results have been combined with those published on the 1990 data. A measurement of the τ polarisation as a function of production angle yields the values for the mean τ polarisation 〈P〉τ=-0.148±0.022 and for the Z0 polarisation PZ=-0.136±0.027. These results are used to determin…

J / psi production in the hadronic decays of the Z.

Abstract: J/psi mesons have been reconstructed from their decay to mu(+)mu(-) and e(+)e(-), using the data collected by the DELPHI experiment during 1991 and 1992 at the LEP collider. From about 1 million hadronic Z decays 153 +/- 17 J/psi were found, 5.4 +/- 2.3 psi' were obtained in the channel J/psi(--> mu(+)mu(-))pi(+)pi(-) and 6.4 +/- 2.7 chi(c) in the channel J/psi(--> mu(+)mu(-))gamma. As the dominant source of J/psi mesons is from b quarks, the following branching ratios: Br(b-->J/psi X) = (1.12 +/- 0.12 (stat.) +/- 0.10 (syst.))%, Br(b --> psi' X) = (0.48 +/- 0.22 (stat.) +/- 0.10 (syst.))%, Br(b-->chi(cl) X) = (1.4 +/- 0.6 (stat.)(-0.2)(+0.4) (syst.))% were measured. From the prop…

Observation of s-Channel Production of Single Top Quarks at the Tevatron

We report the first observation of single-top-quark production in the s channel through the combination of the CDF and D0 measurements of the cross section in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. The data correspond to total integrated luminosities of up to 9.7fb-1 per experiment. The measured cross section is σs=1.29-0.24+0.26pb. The probability of observing a statistical fluctuation of the background to a cross section of the observed size or larger is 1.8×10-10, corresponding to a significance of 6.3 standard deviations for the presence of an s-channel contribution to the production of single-top quarks. © 2014 American Physical Society.

Search for Associated Higgs Boson ProductionWH→WWW*→l±νl′±ν′+Xinpp¯Collisions ats=1.96  TeV

We present a search for associated Higgs boson production in the process $p\bar{p} \to WH\to WWW^*\to l^\pm\nu l'^\pm\nu'+X$ in final states containing two like-sign isolated electrons or muons ($e^\pm e^\pm$, $e^\pm \mu^\pm$, or $\mu^\pm \mu^\pm$). The search is based on D0 Run II data samples corresponding to integrated luminosities of 360--380 pb$^{-1}$. No excess is observed over the predicted standard model background. We set 95% C.L. upper limits on $\sigma(p\bar{p}\to WH)\times Br(H\to WW^*)$ between 3.2 and 2.8 pb for Higgs masses from 115 to 175 GeV.

Search for exclusive charmless b meson decays with the Delphi detector at Lep

Charmless hadronic decays of beauty mesons have been searched for using the data collected with the DELPHI detector at the LEP collider. Several two, three and four-body decay modes have been investigated. Particle identification was used to distinguish the final states with protons, kaons and pions. Three candidate events selected in two-body decay modes are interpreted as evidence for charmless B decays. No excess has been found in higher multiplicity modes and improved upper limits for some of the branching ratios are given. © 1995.

Measurement of the $W$ boson mass with the D0 detector

We give a detailed description of the measurement of the $W$ boson mass, $M_W$, performed on an integrated luminosity of 4.3 fb$^{-1}$, which is based on similar techniques as used for our previous measurement done on an independent data set of 1 fb$^{-1}$ of data. The data were collected using the D0 detector at the Fermilab Tevatron Collider. This data set yields $1.68\times 10^6$ $W\rightarrow e\nu$ candidate events. We measure the mass using the transverse mass, electron transverse momentum, and missing transverse energy distributions. The $M_W$ measurements using the transverse mass and the electron transverse momentum distributions are the most precise of these three and are combined …

Measurement of the electron charge asymmetry inpp¯→W+X→eν+Xdecays inpp¯collisions ats=1.96  TeV

We present a measurement of the electron charge asymmetry in $p\bar{p}\rightarrow W+X \rightarrow e\nu +X$ events at a center-of-mass energy of 1.96 TeV, using data corresponding to 9.7~fb$^{-1}$ of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron pseudorapidity and is presented in five kinematic bins based on the electron transverse energy and the missing transverse energy in the event. The measured asymmetry is compared with next-to-leading-order predictions in perturbative quantum chromodynamics and provides accurate information for the determination of parton distribution functions of the prot…

Measurement of inclusive production of light meson resonances in hadronic decays of the Z0

A study of inclusive production of the meson resonances ρ0, K*0 (892), f{hook}0 (975) and f{hook}2 (1270) in hadronic decays of the Z0 is presented. The measured mean meson multiplicity per hadronic event is 0.83 ± 0.14 for the ρ0 0.64 ± 0.24 for the K*0 (892), 0.10 ± 0.04 for the f{hook}0 (975) in the momentum range p &gt; 0.05pbeam (xp &gt; 0.05) and 0.11 ± 0.05 for the f{hook}2 (1270) for xp &gt; 0.1. These values and the corresponding differential cross sections ( 1 σhadr) dσ dxp for the vector mesons are in good agreement with the predictions of the JETSET 7.3 PS and HERWIG 5.4 models. The f{hook}2 (1270) production is overestimated by HERWIG but its xp-shape is correctly reproduced. T…

Search for Neutral Higgs Bosons in Events with Multiple Bottom Quarks at the Tevatron

The combination of searches performed by the CDF and D0 collaborations at the Fermilab Tevatron Collider for neutral Higgs bosons produced in association with b quarks is reported. The data, corresponding to 2.6fb -1 of integrated luminosity at CDF and 5.2fb -1 at D0, have been collected in final states containing three or more b jets. Upper limits are set on the cross section multiplied by the branching ratio varying between 44 pb and 0.7 pb in the Higgs boson mass range 90 to 300 GeV, assuming production of a narrow scalar boson. Significant enhancements to the production of Higgs bosons can be found in theories beyond the standard model, for example, in supersymmetry. The results are int…

Study of the decayBs0→J/ψf2′(1525)inμ+μ−K+K−final states

We investigate the decay $B_s^0 \rightarrow J/\psi K^+ K^-$ for invariant masses of the $K^+K^-$ pair in the range $1.35

Evidence for Zc±(3900) in semi-inclusive decays of b -flavored hadrons

We present evidence for the exotic charged charmoniumlike state Zc±(3900) decaying to J/ψπ± in semi-inclusive weak decays of b-flavored hadrons. The signal is correlated with a parent J/ψπ+π- system in the invariant-mass range 4.2-4.7 GeV that would include the exotic structure Y(4260). The study is based on 10.4 fb-1 of pp collision data collected by the D0 experiment at the Fermilab Tevatron collider. © 2018 authors. Published by the American Physical Society.

Dependence of the tt¯ production cross section on the transverse momentum of the top quark

We present a measurement of the differential cross section for $t\bar{t}$ events produced in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV as a function of the transverse momentum ($p_T$) of the top quark. The selected events contain a high-$p_T$ lepton ($\ell$), four or more jets, and a large imbalance in $p_T$, and correspond to 1 fb${}^{-1}$ of integrated luminosity recorded with the D0 detector. Each event must have at least one candidate for a $b$ jet. Objects in the event are associated through a constrained kinematic fit to the $t\bar{t}\to WbW\bar{b} \to \ell\nu b q\bar{q}'\bar{b}$ process. Results from next-to-leading-order perturbative QCD calculations agree with the measured diffe…

Measurement of color flow intt¯events frompp¯collisions ats=1.96  TeV

We present the first measurement of the color representation of the hadronically decaying W boson in t-tbar events, from 5.3 fb^-1 of integrated luminosity collected with the D0 experiment. A novel calorimeter-based vectorial variable, "jet pull," is used, sensitive to the color-flow structure of the final state. We find that the fraction of uncolored W bosons is 0.56 +- 0.42(stat+syst), in agreement with the standard model.

Measurements of inclusive W+jets production rates as a function of jet transverse momentum in pp¯ collisions at s=1.96 TeV

This Letter describes measurements of inclusive W (--> e nu) + n jet cross sections (n = 1-4), presented as total inclusive cross sections and differentially in the nth jet transverse momentum. The measurements are made using data corresponding to an integrated luminosity of 4.2 fb-1 collected by the D0 detector at the Fermilab Tevatron Collider, and achieve considerably smaller uncertainties on W +jets production cross sections than previous measurements. The measurements are compared to next-to-leading order perturbative QCD (pQCD) calculations in the n =1-3 jet multiplicity bins and to leading order pQCD calculations in the 4-jet bin. The measurements are generally in agreement with pQCD…

Search for excited muons inpp¯collisions ats=1.96  TeV

We present the results of a search for the production of an excited state of the muon, mu(*), in proton antiproton collisions at root s =1.96 TeV. The data have been collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 380 pb(-1). We search for mu(*) in the process p (p) over bar ->mu(*)mu, with the mu(*) subsequently decaying to a muon plus photon. No excess above the standard model expectation is observed in data. Interpreting our data in the context of a model that describes mu(*) production by four-fermion contact interactions and mu(*) decay via electroweak processes, we set a 95% confidence level production cros…

Search for the standard model Higgs boson in tau final states

We present a search for the standard model Higgs boson using hadronically decaying tau leptons, in 1 inverse femtobarn of data collected with the D0 detector at the Fermilab Tevatron ppbar collider. We select two final states: tau plus missing transverse energy and b jets, and tau+ tau- plus jets. These final states are sensitive to a combination of associated W/Z boson plus Higgs boson, vector boson fusion and gluon-gluon fusion production processes. The observed ratio of the combined limit on the Higgs production cross section at the 95% C.L. to the standard model expectation is 29 for a Higgs boson mass of 115 GeV.

Search forZγevents with large missing transverse energy inpp¯collisions ats=1.96  TeV

We present the first search for new phenomena in Z gamma final states with large missing transverse energy using data corresponding to an integrated luminosity of 6.2 fb(-1) collected with the D0 experiment in p (p) over bar collisions at root s 1.96 TeV. This signature is predicted in gauge-mediated supersymmetry-breaking models, where the lightest neutralino (chi) over tilde (0)(1) is the next-to-lightest supersymmetric particle and is produced in pairs, possibly through decay from heavier supersymmetric particles. The (chi) over tilde (0)(1) can decay either to a Z boson or a photon and an associated gravitino that escapes detection. We exclude this model at the 95% C.L. for supersymmetr…

Multivariate searches for single top quark production with the D0 detector

We present a search for electroweak production of single top quarks in the s-channel (p-pbar -&gt; t bbar + X) and t-channel (p-pbar -&gt; tq bbar + X) modes. We have analyzed 230 pb^(-1) of data collected with the D0 detector at the Fermilab Tevatron collider at a center-of-mass energy of sqrt(s) = 1.96 TeV. Two separate analysis methods are used: neural networks and a cut-based analysis. No evidence for a single top quark signal is found. We set 95% confidence level upper limits on the production cross sections using Bayesian statistics, based on event counts and binned likelihoods formed from the neural network output. The limits from the neural network (cut-based) analysis are 6.4 pb (1…

Measurement of the top-quark mass inpp¯collisions using events with two leptons

Made available in DSpace on 2022-04-29T05:11:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-09-26 We present a measurement of the top-quark mass (m t) in pp̄ collisions at √s=1.96TeV using tt̄ events with two leptons (ee, eμ, or μμ) and accompanying jets in 4.3fb -1 of data collected with the D0 detector at the Fermilab Tevatron collider. We analyze the kinematically underconstrained dilepton events by integrating over their neutrino rapidity distributions. We reduce the dominant systematic uncertainties from the calibration of jet energy using a correction obtained from tt̄ events with a final state of a single lepton plus jets. We also correct jets in simulated events to replic…

Measurement of the inclusive charmless and double-charm B branching ratios

The DELPHI experiment at LEP has measured the inclusive charmless B hadron decay branching ratio, the B branching ratio into two charmed particles, and the total number of charmed particles per B decay, using the hadronic Z data taken between 1992 and 1995. The results are extracted from a fit to the b-tagging probability distribution based on the precise impact parameter measurements made using the microvertex detector. The inclusive charmless B branching ratio, including B decays into hidden charm (c (c) over bar), is measured to be 0.033 +/- 0.021. The B branching ratio into two open charmed particles is 0.136 +/- 0.042. The mean number of charmed particles per B decay (including hidden …

Measurement of the differential cross section of photon plus jet production inpp¯collisions ats=1.96  TeV

We study the process of associated photon and jet production, p (p) over bar -> gamma + jet + X, using 8.7 fb(-1) of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy root s = 1.96 TeV. Photons are reconstructed with rapidity vertical bar y(gamma)vertical bar 20 GeV. The highest-p(T) jet is required to be in one of four rapidity regions up to vertical bar y(jet)vertical bar 0) and opposite signs (y(gamma)y(jet) <= 0) of photon and jet rapidities. We compare the measured triple-differential cross sections, d(3)sigma/dp(T)(gamma)dy(gamma)dy(jet), to next-to-leading order (NLO) perturbative QCD calculations using different sets of p…

Measurement of theΛb0lifetime in the exclusive decayΛb0→J/ψΛ0inpp¯collisions ats=1.96  TeV

We measure the Lambda_b^0 lifetime in the fully reconstructed decay Lambda_b^0 -> J/psi Lambda^0 using 10.4 fb^-1 of ppbar collisions collected with the D0 detector at sqrt(s)=1.96 TeV. The lifetime of the topologically similar decay channel B^0 -> J/psi K^0_S is also measured. We obtain tau(Lambda_b^0) = 1.303 +- 0.075 (stat.) +- 0.035 (syst.) ps and tau(B^0) = 1.508 +- 0.025 (stat.) +- 0.043 (syst.) ps. Using these measurements, we determine the lifetime ratio of tau(Lambda_b^0)/tau(B^0) = 0.864 +- 0.052 (stat.) +- 0.033 (syst.).

First evidence for a charm radial excitation, D

Using D*+ mesons exclusively reconstructed in the DELPHI detector at LEP, an excess of 66 +/- 14(stat.) events is observed in the D(*+)pi(+)pi(-) final state with a mass of 2637 +/- 2(stat.) +/- 6(syst.) MeV/c(2) and a full width smaller than 15 MeV/c(2) (95% C.L.). This signal is compatible with the expected decay of a radially excited D*' (J(P) = 1(-))meson. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

A comparison of jet production rates on the Z0 resonance to perturbative QCD

The production rates for 2-, 3-, 4- and 5-jet hadronic final states have been measured with the DELPHI detector at the e+e- storage ring LEP at centre of mass energies around 91.5 GeV. Fully corrected data are compared to O(αs 2) QCD matrix element calculations and the QCD scale parameter ΛMS is determined for different parametrizations of the renormalization scale μ2. Including all uncertainties our result is αs(MZ 2)=0.114±0.003[stat.]±0.004[syst.]±0.012[theor.] .

Measurement of differential Z/γ∗+jet+X cross sections in pp¯ collisions at s=1.96 TeV

We present new measurements of differential cross sections for Z/gamma*(->mumu)+jet+X production in a 1 fb-1 data sample collected with the D0 detector in proton anti-proton collisions at sqrt{s}=1.96 TeV. Results include the first measurements differential in the Z/gamma* transverse momentum and rapidity, as well as new measurements differential in the leading jet transverse momentum and rapidity. Next-to-leading order perturbative QCD predictions are compared to the measurements, and reasonable agreement is observed, except in the region of low Z/gamma* transverse momentum. Predictions from two event generators based on matrix elements and parton showers, and one pure parton shower event …

Search for pair production of heavy objects in 4-jet events at sqrt {s}$=130-136 GeV

Results are presented of a search for pair production of heavy objects decaying into four hadronic jets, as expected for example from associated or pair production of MSSM Higgs bosons, hA or H$^+$H$^-$, using a data sample of $5.9\,$pb$^{-1}$ of $e^+ e^-$ collisions at $\sqrt{s}=130$-$136\,{\mathrm {GeV}}$ collected with the DELPHI detector at LEP in November 1995. The data and expectations from standard processes agree after four-jet selections. An analysis based on $b$-tagging finds no hA candidate with high mass. A study optimized to search for H$^+$H$^-$ events with mass in the 40-50$\,{\mathrm{GeV}}/c^2$ range also finds no candidate. Finally a comparison is made with a recent ALEPH a…

Search for pair production of the scalar top quark in the electron-muon final state

We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ($\tilde{t}_1$) in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider corresponding to an integrated luminosity of 5.4 fb$^{-1}$. The scalar top quarks are assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tilde{\nu}$), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected, and improved exclusion limits at the 95% C.L. are set in the the ($M_{\tilde{t}_1}$,$M_{\tilde{\nu}}$) mass plane.

Search for Higgs bosons decaying to τ+τ− pairs in pp¯ collisions at s=1.96 TeV

Abstract We present a search for the production of neutral Higgs bosons decaying into τ + τ − pairs in p p ¯ collisions at a center-of-mass energy of 1.96 TeV. The data, corresponding to an integrated luminosity of 5.4 fb−1, were collected by the D0 experiment at the Fermilab Tevatron Collider. We set upper limits at the 95% C.L. on the product of production cross section and branching ratio for a scalar resonance decaying into τ + τ − pairs, and we interpret these limits as limits on the production of Higgs bosons in the minimal supersymmetric standard model (MSSM) and as constraints in the MSSM parameter space.

A measurement of the tau lifetime

The tau lepton lifetime is measured using four different methods with the DELPHI detector. Three measurements using one prong decays are combined, accounting for correlations, resulting in tau(tau) = 298 +/- 7 (stat.) +/- 4 (syst.) fs while the decay length distribution of three prong decays gives tau(tau) = 298 +/- 13 (stat.) +/- 5 (syst.) fs. The combined result is tau(tau) = 298 +/- 7 fs. The ratio of the Fermi coupling constant from tau decay relative to that from muon decay is found to be 0.985 +/- 0.013, compatible with lepton universality.

Combination of CDF and D0 W-Boson mass measurements

We summarize and combine direct measurements of the mass of the W boson in √s=1.96 TeV proton-antiproton collision data collected by CDF and D0 experiments at the Fermilab Tevatron Collider. Earlier measurements from CDF and D0 are combined with the two latest, more precise measurements: a CDF measurement in the electron and muon channels using data corresponding to 2.2 fb-1 of integrated luminosity, and a D0 measurement in the electron channel using data corresponding to 4.3 fb-1 of integrated luminosity. The resulting Tevatron average for the mass of the W boson is M W=80387±16 MeV. Including measurements obtained in electron-positron collisions at LEP yields the most precise value of M W…

First measurement of f′2 (1525) production in Z0 hadronic decays

The inclusive production of the f(2)'(1525) in hadronic Z(0) decays has been studied in data collected by the DELPHI detector at LEP. The Ring Imaging Cherenkov detectors were important tools in the identification of the decay f(2)'(1525) --> K+K-. The average number of f(2)(')(1525) produced per hadronic Z decay, [f(2)'] = 0.020 +/- 0.005 (stat) +/- 0.006 (syst), and the momentum distribution of the f(2)'(1525) have both been measured. The mass and width of the f(2)'(1525) are found to be [M(f2)'] = 1535 +/- 5 (stat) +/- 4 (syst) MeV/c(2). [Gamma(f2)'] = 60 +/- 20 (stat) +/- 19 (syst) MeV/c(2)

Improved $b$ quark jet identification at the D0 experiment

The ability to identify jets which originated from $b$ quarks is an important tool of the physics program of the D0 experiment at the Fermilab Tevatron $p\bar{p}$ collider. This article describes a new algorithm designed to select jets originating from $b$ quarks while suppressing the contamination caused by jets from other quark flavors and gluons. Additionally, a new technique, the SystemN method, for determining the misidentification rate directly from data is presented.

The upgraded DO detector

The DØ experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid-argon calorimeters and central muon detector, remaining from Run I, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of s…

Energy dependence of inclusive spectra in e+ e- annihilation

Inclusive charged hadron distributions as obtained from the DELPHI measurements at 130, 136, 161, 172 and 183 GeV are presented as a function of the variables rapidity, xi(p), p and transversal momenta. Data are compared with event generators and with MLLA calculations, in order to examine the hypothesis of local parton hadron duality. The differential momentum spectra show an indication for coherence effects in the production of soft particles. The relation between the energy dependence of the charged multiplicity and the rapidity distribution is examined. (C) 1999 Elsevier Science B.V. All rights reserved.

Measurement of the combined rapidity and pT dependence of dijet azimuthal decorrelations in pp¯ collisions at s=1.96 TeV

We present the first combined measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations, using the recently proposed quantity R-Delta phi. The variable R-Delta phi measures the fraction of the inclusive dijet events in which the azimuthal separation of the two jets with the highest transverse momenta is less than a specified value of the parameter Delta phi(max). The quantity R-Delta phi is measured in p (p) over bar collisions at root s = 1.96 TeV, as a function of the dijet rapidity interval, the total scalar transverse momentum, and Delta phi(max). The measurement uses an event sample corresponding to an integrated luminosity of 0.7 fb(-1) collected…

Search for the Standard Model Higgs Boson in theH→WW→lνq′q¯Decay Channel

We present a search for the standard model Higgs boson (H) in ppbar collisions at sqrt{s}=1.96 TeV in events containing a charged lepton (ell), missing transverse energy, and at least two jets, using 5.4 fb^-1 of integrated luminosity recorded with the D0 detector at the Fermilab Tevatron Collider. This analysis is sensitive primarily to Higgs bosons produced through the fusion of two gluons or two electroweak bosons, with subsequent decay H->WW->ell+nu+q'qbar, where ell is an electron or muon. The search is also sensitive to contributions from other production channels, such as WH->ell+nu+bbbar In the absence of signal, we set limits at the 95% C.L. on the cross section for H production si…

Measurement of the Angular and Lifetime Parameters of the DecaysBd0→J/ψK*0andBs0→J/ψϕ

We present measurements of the linear polarization amplitudes and the strong relative phases that describe the flavor-untagged decays $B_{d}^{0}\to J/\psi K^{*0}$ and $B_{s}^{0}\to J/\psi\phi$ in the transversity basis. We also measure the mean lifetime $\bar{\tau}_{s}$ of the $B_{s}^{0}$ mass eigenstates and the lifetime ratio $\bar{\tau}_{s}/\tau_{d}$. The analyses are based on approximately 2.8 fb$^{-1}$ of data recorded with the D0 detector. From our measurements of the angular parameters we conclude that there is no evidence for a deviation from flavor SU(3) symmetry for these decays and that the factorization assumption is not valid for the $B_{d}^{0}\to J/\psi K^{*0}$ decay.

Search for pair production of first-generation leptoquarks in pp¯ collisions at s=1.96 TeV

A search for pair production of first-generation leptoquarks LQ is performed with data collected by the D0 experiment in p pbar collisions at sqrt(s)=1.96 TeV at the Fermilab Tevatron Collider. In a sample of data corresponding to ~1 fb-1, the search has been performed on the final states with two electrons and two jets or one electron, two jets and missing transverse energy. We find our data consistent with standard model expectations. The results are combined with those found in a previous analysis of events with two jets and missing transverse energy to obtain scalar LQ mass limits. We set 95% C.L. lower limits on a scalar LQ mass of 299 GeV, 284 GeV and 216 GeV for beta=1, beta=0.5 and …

Observation and studies of double J/psi production at the Tevatron

We present the observation of doubly-produced $J/\psi$ mesons with the D0 detector at Fermilab in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV. The production cross section for both singly and doubly-produced $J/\psi$ mesons is measured using a sample with an integrated luminosity of 8.1fb$^{-1}$. For the first time, the double $J/\psi$ production cross section is separated into contributions due to single and double parton scatterings. Using these measurements, we determine the effective cross section $\sigma_{eff}$, a parameter characterizing an effective spatial area of the parton-parton interactions and related to the parton spatial density inside the nucleon.

Measurement of the top quark mass in thelepton+jetsfinal state with the matrix element method

We present a measurement of the top quark mass with the Matrix Element method in the lepton+jets final state. As the energy scale for calorimeter jets represents the dominant source of systematic uncertainty, the Matrix Element likelihood is extended by an additional parameter, which is defined as a global multiplicative factor applied to the standard energy scale. The top quark mass is obtained from a fit that yields the combined statistical and systematic jet energy scale uncertainty.

Study ofZγEvents and Limits on AnomalousZZγandZγγCouplings inpp¯Collisions ats=1.96  TeV

We present a measurement of the Z gamma production cross section and limits on anomalous ZZ gamma and Z gamma gamma couplings for form-factor scales of Lambda=750 and 1000 GeV. The measurement is based on 138 (152) candidates in the ee gamma (mu mu gamma) final state using 320(290) pb(-1) of p (p) over bar collisions at root s=1.96 TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are vertical bar h(10,30)(Z)vertical bar < 0.23, vertical bar h(20,40)(Z)vertical bar < 0.020, vertical bar h(10,30)(gamma)vertical bar < 0.23, and vertical bar h(20,40)(gamma)vertical bar < 0.019 for Lambda=1000 GeV.

Measurement of the semileptonic charge asymmetry in B-0 meson mixing with the D0 detector

We present a measurement of the semileptonic mixing asymmetry for B0 mesons, a^d_{sl}, using two independent decay channels: B0 -&gt; mu+D-X, with D- -&gt; K+pi-pi-; and B0 -&gt; mu+D*-X, with D*- -&gt; antiD0 pi-, antiD0 -&gt; K+pi- (and charge conjugate processes). We use a data sample corresponding to 10.4 fb^{-1} of ppbar collisions at sqrt(s) = 1.96 TeV, collected with the D0 experiment at the Fermilab Tevatron collider. We extract the charge asymmetries in these two channels as a function of the visible proper decay length (VPDL) of the B0 meson, correct for detector-related asymmetries using data-driven methods, and account for dilution from charge-symmetric processes using Monte Car…

Measurement of the electric charge of the top quark intt¯events

We present a measurement of the electric charge of top quarks using t (t) over bar events produced in p (p) over bar collisions at the Tevatron. The analysis is based on fully reconstructed t (t) over bar pairs in lepton + jets final states. Using data corresponding to 5.3 fb(-1) of integrated luminosity, we exclude the hypothesis that the top quark has a charge of Q = -4/3e at a significance greater than 5 standard deviations. We also place an upper limit of 0.46 on the fraction of such quarks that can be present in an admixture with the standard model top quarks (Q = +2/3e) at a 95% confidence level.

Measurement of the charge asymmetry in semileptonic Bs0 decays.

Made available in DSpace on 2022-04-28T20:16:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-04-11 We have performed the first direct measurement of the time-integrated flavor untagged charge asymmetry in semileptonic Bs0 decays ASLs,unt by comparing the decay rate of Bs0→μ+Ds-νX, where Ds- π- and →K+K-, with the charge-conjugate B̄s0 decay rate. This sample was selected from 1.3fb-1 of data collected by the D0 experiment in run II of the Fermilab Tevatron collider. We obtain ASLs,unt=[1.23±0.97(stat)±0. 17(syst)]×10-2. Assuming that Δms/Γ̄s 1, this result can be translated into a measurement of the CP-violating phase in Bs0 mixing: ΔΓs/Δmstan s=[2.45±1.93(stat)±0.35(syst)] ×10-2.…

Precision Measurement of the Top Quark Mass in &lt;span class="aps-inline-formula"&gt;&lt;math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"&gt;&lt;mrow&gt;&lt;mstyle mathvariant="normal"&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mstyle&gt;&lt;mtext mathvariant="bold"&gt;epton&lt;/mtext&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mstyle mathvariant="normal"&gt;&lt;mi&gt;J&lt;/mi&gt;&lt;/mstyle&gt;&lt;mtext mathvariant="bold"&gt;ets&lt;/mtext&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; Final States

We measure the mass of the top quark in lepton$+$jets final states using the full sample of $$p\bar{p}$$ collision data collected by the D0 experiment in Run II of the Fermilab Tevatron Collider at $$\sqrt s=1.96 $$TeV, corresponding to $$9.7 {\rm fb}^{-1}$$ of integrated luminosity. We use a matrix element technique that calculates the probabilities for each event to result from $$t\bar t$$ production or background. The overall jet energy scale is constrained in situ by the mass of the $W$ boson. We measure $$m_t=174.98\pm0.76$$ GeV. In conclusion, this constitutes the most precise single measurement of the top-quark mass.

Search for supersymmetry via associated production of charginos and neutralinos in final states with three leptons

A search for associated production of charginos and neutralinos is performed using data recorded with the D0 detector at a ppbar center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider. This analysis considers final states with missing transverse energy and three leptons, of which at least two are electrons or muons. No evidence for supersymmetry is found in a dataset corresponding to an integrated luminosity of 320 pb-1. Limits on the product of the production cross section and leptonic branching fraction are set. For the minimal supergravity model, a chargino lower mass limit of 117 GeV at the 95% C.L. is derived in regions of parameter space with enhanced leptonic branching f…

Search for Higgs boson production in oppositely charged dilepton and missing energy final states in9.7  fb−1ofpp¯collisions ats=1.96  TeV

We present a search for Higgs boson in final states with two oppositely charged leptons and large missing transverse energy as expected in H -> WW -> lvlv decays. The events are selected from the full Run II data sample of 9.7 fb-1 of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider at sqrt s = 1.96 TeV. To validate our search methodology, we measure the non-resonant W W production cross section and find sigma_WW = 11.6 +/- 0.7 pb, in agreement with the standard model prediction. In the Higgs boson search, no significant excess above the background expectation is observed. Upper limits at the 95% confidence level on the Higgs boson production cross section a…

Search for dark photons from supersymmetric hidden valleys

We search for a new light gauge boson, a dark photon, with the D0 experiment. In the model we consider, supersymmetric partners are pair produced and cascade to lightest neutralinos that can decay into the hidden sector state plus either a photon or a dark photon. The dark photon decays through its mixing with a photon into fermion pairs. We therefore investigate a previously unexplored final state that contains a photon, two spatially close leptons, and large missing transverse energy. We do not observe any evidence for dark photons and set a limit on their production.

Search for promptly produced heavy quarkonium states in hadronic Z decays

A search has been made for direct production of heavy quarkonium states in more than 3 million hadronic Z^{0} decays in the 1991-1994 DELPHI data. Prompt J/\psi, \psi(2S) and \Upsilon candidates have been searched for through their leptonic decay modes using criteria based on the kinematics and decay vertex positions. New upper limits are set at the 90 \% confidence level for {Br( Z^0 \rightarrow \left( Q \bar{Q} \right) X ) / Br( Z^0 \rightarrow \mbox{hadrons})} for various strong production mechanisms of J/\psi and \Upsilon; these range down to 0.9 \times 10^{-4}. The limits are set in the presence of a small excess (\sim 1 \% statistical probability of a background fluctuation) in the su…

Inclusive Production of theX(4140)State inpp¯Collisions at D0

We present a study of the inclusive production of the $X(4140)$ with the decay to the $J/\psi \phi$ final state in hadronic collisions. Based on $10.4~\rm{fb^{-1}}$ of $p \overline p $ collision data collected by the D0 experiment at the Fermilab Tevatron collider, we report the first evidence for the prompt production of $X(4140)$ and find the fraction of $X(4140)$ events originating from $b$ hadrons to be $f_b=0.39\pm 0.07 {\rm \thinspace (stat)} \pm 0.10 {\rm \thinspace (syst)} $. The ratio of the non-prompt $X(4140)$ production rate to the $B_s^0$ yield in the same channel is $R=0.19 \pm 0.05 {\rm \thinspace (stat)} \pm 0.07 {\rm \thinspace (syst)}$. The values of the mass $M=4152.5 \pm…

Measurement of differentialtt¯production cross sections inpp¯collisions

The production of top quark-antiquark pair events in pp collisions at root s= 1.96 TeV is studied as a function of the transverse momentum and absolute value of the rapidity of the top quarks as well as of the invariant mass of the tt pair. We select events containing an isolated lepton, a large imbalance in transverse momentum, and four or more jets with at least one jet identified as originating from a b quark. The data sample corresponds to 9.7 fb(-1) of integrated luminosity recorded with the D0 detector during Run II of the Fermilab Tevatron Collider. Observed differential cross sections are consistent with standard model predictions.

Search for a Fourth Generationt′Quark inpp¯Collisions ats=1.96  TeV

We present a search for pair production of a fourth generation t' quark and its antiparticle, followed by their decays to a W boson and a jet, based on an integrated luminosity of 5.3/fb of proton-antiproton collisions at sqrt{s}=1.96 TeV collected by the D0 Collaboration at the Fermilab Tevatron Collider. We set upper limits on the t't'bar production cross section that exclude at the 95% C.L. a t' quark that decays exclusively to W+jet with a mass below 285 GeV. We observe a small excess in the muon+jets channel which reduces the mass range excluded compared to the expected limit of 320 GeV in the absence of a signal.

Combination of the top-quark mass measurements from the Tevatron collider

Aaltonen, T. et al.

Combination of D0 measurements of the top quark mass

We present a combination of measurements of the top quark mass by the D0 experiment in the lepton+jets and dilepton channels. We use all the data collected in Run I (1992--1996) at $\sqrt s=1.8$ TeV and Run II (2001--2011) at $\sqrt s=1.96$ TeV of the Tevatron $p \bar{p}$ collider, corresponding to integrated luminosities of 0.1 fb$^{-1}$ and 9.7 fb$^{-1}$, respectively. The combined result is: $m_t = 174.95 \pm0.40\,{\rm(stat)} \pm 0.64\,{\rm(syst)}\,{\rm{GeV}}=174.95 \pm 0.75 \, {\rm{GeV}}$.

Search for the Standard Model Higgs Boson in the Missing Energy and Acoplanarb-Jet Topology ats=1.96  TeV

We report a search for the standard model Higgs boson in the missing energy and acoplanar b-jet topology, using an integrated luminosity of 0.93 fb(-1) recorded by the D0 detector at the Fermilab Tevatron p (p) over bar Collider. The analysis includes signal contributions from p (p) over bar -> ZH -> v (v) over barb (b) over bar, as well as from WH production in which the charged lepton from the W boson decay is undetected. Neural networks are used to separate signal from background. In the absence of a signal, we set limits on sigma(p (p) over bar -> VH) x B(H -> b (b) over bar) at the 95% C.L. of 2.6-2.3 pb, for Higgs boson masses in the range 105-135 GeV, where V W, Z. The corresponding …

WγProduction and Limits on AnomalousWWγCouplings inpp¯Collisions ats=1.96  TeV

We measure the cross section and the difference in rapidities between photons and charged leptons for inclusive W -> lnu+gamma production in egamma and mugamma final states. Using data corresponding to an integrated luminosity of 4.2 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider, the cross section multiplied by the branching fraction for the process ppbar -> Wgamma+X -> lnugamma+X, measured to be 15.8 +/- 0.8 (stat.) +/- 1.2 (syst.) pb, and the distribution of the charge-signed photon-lepton rapidity difference are found to be in agreement with the standard model. These results provide the most stringent limits on anomalous WWgamma couplings for data from hadron coll…

Simultaneous Measurement of the RatioR=B(t→Wb)/B(t→Wq)and the Top-Quark Pair Production Cross Section with the D0 Detector ats=1.96  TeV

We present the first simultaneous measurement of the ratio of branching fractions, R = B(t --> Wb)/B(t --> Wq), with q being a d, s, or b quark, and the top-quark pair production cross section sigma(t (t) over bar) in the lepton plus jets channel using 0.9 fb(-1) of p (p) over bar collision data at root s = 1.96 TeV collected with the D0 detector. We extract R and sigma(t (t) over bar) by analyzing samples of events with 0, 1, and >= 2 identified b jets. We measure R = 0.97(-0.08)(+0.09) (stat + syst) and sigma(t (t) over bar) = 8.18(-0.84)(+0.90) (stat + syst) +/- 0.50(lumi) pb, in agreement with the standard model prediction.

Search for Neutral Higgs Bosons in Multi-b-Jet Events inpp¯Collisions ats=1.96  TeV

Data recorded by the D0 experiment at the Fermilab Tevatron Collider are analyzed to search for neutral Higgs bosons produced in association with b quarks. This production mode can be enhanced in the minimal supersymmetric standard model (MSSM). The search is performed in the three b quark channel using multijet triggered events corresponding to an integrated luminosity of 1 fb(-1). No statistically significant excess of events with respect to the predicted background is observed and limits are set in the MSSM parameter space.

Studies ofWboson plus jets production inpp¯collisions ats=1.96  TeV

We present a comprehensive analysis of inclusive W(-> ev) + n-jet (n >= 1, 2, 3, 4) production in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV at the Tevatron collider using a 3.7 fb(-1) data set collected by the D0 detector. Differential cross sections are presented as a function of the jet rapidities (y), lepton transverse momentum (P-T) and pseudorapidity (eta), the scalar sum of the transverse energies of the W boson and all jets (H-T), leading dijet P-T and invariant mass, dijet rapidity separations for a variety of jet pairings for P-T-ordered and angular-ordered jets, dijet opening angle, dijet azimuthal angular separations for P-T-ordered and angular-ordered j…

Evidence for Spin correlation in tt̄ production

Made available in DSpace on 2022-04-29T03:09:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-01-19 We present a measurement of the ratio of events with correlated t and t̄ spins to the total number of tt̄ events. This ratio f is evaluated using a matrix-element-based approach in 729 tt̄ candidate events with a single lepton (electron or muon) and at least four jets. The analyzed pp̄ collisions data correspond to an integrated luminosity of 5.3fb -1 and were collected with the D0 detector at the Fermilab Tevatron collider operating at a center-of-mass energy √s=1.96TeV. Combining this result with a recent measurement of f in dileptonic final states, we find f in agreement with the …

Search for flavor changing neutral currents in decays of top quarks

We present a search for flavor changing neutral currents in decays of top quarks. The analysis is based on a search for ttbar -&gt; l'null + jets (l, l' = e, mu) final states using 4.1 fb^-1 of integrated luminosity of ppbar collisions at sqrt(s) = 1.96 TeV. We extract limits on the branching ratio B(t -&gt; Zq) (q = u, c quarks), assuming anomalous tuZ or tcZ couplings. We do not observe any sign of such anomalous coupling and set a limit of B &lt; 3.2% at 95% C.L.

Measurement of theBs0Lifetime in the Flavor-Specific Decay ChannelBs0→Ds−μ+νX

We present an updated measurement of the B-s(0) lifetime using the semileptonic decays B-s(0) -> D-s(-)mu(+)nu X, with D-s(-) -> phi pi(-) and phi -> K+K- (and the charge conjugate process). This measurement uses the full Tevatron Run II sample of proton-antiproton collisions at root s = 1.96 TeV, comprising an integrated luminosity of 10.4 fb(-1). We find a flavor-specific lifetime tau(fs)(B-s(0)) = 1.479 +/- 0.010(stat) +/- 0.021(syst) ps. This technique is also used to determine the B-0 lifetime using the analogous B-0 -> D- mu(+)nu X decay with D- -> phi pi(-) and phi -> K+K-, yielding tau(B-0) = 1.534 +/- 0.019(stat) +/- 0.021(syst) ps. Both measurements are consistent with the current…

Measurement of spin correlation in tt¯ production using dilepton final states

We measure the correlation between the spin of the top quark and the spin of the anti-top quark in (ttbar -> W+ W- b bbar -> l+ nu b l- nubar bbar) final states produced in ppbar collisions at a center of mass energy sqrt(s)=1.96 TeV, where l is an electron or muon. The data correspond to an integrated luminosity of 5.4 fb-1 and were collected with the D0 detector at the Fermilab Tevatron collider. The correlation is extracted from the angles of the two leptons in the t and tbar rest frames, yielding a correlation strength C= 0.10^{+0.45}_{-0.45}, in agreement with the NLO QCD prediction within two standard deviations, but also in agreement with the no correlation hypothesis.

A Precise Measurement of the Tau Lepton Lifetime

The tau lepton lifetime has been measured using three different methods with the DELPHI detector. Two measurements of one-prong decays are combined, accounting for correlations, giving a result of \tau_\tau = 291.8 \pm 3.3 \mbox{ (stat.)} \pm 2.0 \mbox{(sys.) fs} while the decay length distribution of three-prong decays gives the result \tau_{\tau} = 286.7 \pm 4.9 \mbox{ (stat.)} \pm 3.3 \mbox{ (sys.) fs}. Combining the results presented here with previous DELPHI measurements, we get \tau_{\tau} = 291.4 \pm 3.0 fs and find that the ratio of the coupling constant for tau decay relative to that for muon decay is 0.990 \pm 0.009, compatible with lepton universality.

A search for invisible Higgs bosons produced in e+e- interactions at LEP 2 energies

Searches for HZ production with the Higgs boson decaying into an invisible final state have been performed with the data collected by the DELPHI experiment up to the centre-of-mass energy of 183 GeV. The hadronic and muon pair final states of the Z boson were analysed. From the absence of signal, upper limits on the cross-section and the corresponding Higgs boson mass limits were set at 95% confidence level. The results are interpreted as excluded parameter regions in the framework of the minimal supersymmetric standard model and in the simplest Majoron model with one Higgs doublet and one Higgs singlet field. (C) 1999 Elsevier Science B.V. All rights reserved.

Strange baryon production in Z hadronic decays

A study of the production of strange octet and decuplet baryons in hadronic decays of the Z recorded by the DELPHI detector at LEP is presented. This includes the first measurement of the ∑± average multiplicity. The total and differential cross sections, the event topology and the baryon-antibaryon correlations are compared with current hadronization models. © 1995 Springer-Verlag.

Direct limits on the $B_s^0$ oscillation frequency

Made available in DSpace on 2022-04-28T20:09:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-01-01 We report results of a study of the Bs0 oscillation frequency using a large sample of Bs0 semileptonic decays corresponding to approximately 1fb-1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider in 2002-2006. The amplitude method gives a lower limit on the Bs0 oscillation frequency at 14.8ps-1 at the 95% C.L. At Δms=19ps-1, the amplitude deviates from the hypothesis A=0 (1) by 2.5 (1.6) standard deviations, corresponding to a two-sided C.L. of 1% (10%). A likelihood scan over the oscillation frequency, Δms, gives a most probable value of 19ps…

Search for universal extra dimensions in ppbar collisions

We present a search for Kaluza-Klein (KK) particles predicted by models with universal extra dimensions (UED) using a data set corresponding to an integrated luminosity of 7.3 fb$^{-1}$, collected by the D0 detector at a $p\bar p$ center of mass energy of 1.96 TeV. The decay chain of KK particles can lead to a final state with two muons of the same charge. This signature is used to set a lower limit on the compactification scale of $R^{-1}&gt;260$ GeV in a minimal UED model.

Search for chargino pair production in scenarios with gravitino LSP and stau NLSP at GeV at LEP

Promptly decaying lightest charginos were searched for in the context of scenarios with gravitino LSP. It was assumed that the stau is the next to lightest supersymmetric particle (NLSP). Data collected with the DELPHI detector at a centre-of-mass energy near 183~{~mbox{${mathrm{GeV}}$}}\nwere analysed combining the methods developed in previous searches. No evidence for the production of these particles was found. Hence, limits were derived at 95% confidence level. The mass of charginos was found to be greater than 85.5~GeV/$c^2$ for $m_{ ilde{chi}^+_1}-m_{ ilde{ au}_1}geq 0.3 {mathrm{GeV}}/c^2$, independently of the mass of the gravitino.

Azimuthal decorrelations and multiple parton interactions inγ+2jet andγ+3jet events inpp¯collisions ats=1.96  TeV

Samples of inclusive photon+2 jet and photon+3 jet events collected by the D0 experiment with an integrated luminosity of about 1fb^-1 in ppbar collisions at sqrt{s}=1.96 TeV are used to measure cross sections as a function of the angle in the plane transverse to the beam direction between the transverse momentum (pT) of the photon+leading jet system (jets are ordered in pT) and pT of the other jet for photon+2 jet, or pT sum of the two other jets for photon+3 jet events. The results are compared to different models of multiple parton interactions (MPI) in the PYTHIA and SHERPA Monte Carlo (MC) generators. The data indicate a contribution from events with double parton (DP) interactions and…

Zγproduction and limits on anomalousZZγandZγγcouplings inpp¯collisions ats=1.96  TeV

We present a measurement of ppbar->Zgamma->ll+gamma (l = e, mu) production with a data sample corresponding to an integrated luminosity of 6.2 fb^{-1} collected by the D0 detector at the Fermilab Tevatron ppbar Collider. The results of the electron and muon channels are combined, and we measure the total production cross section and the differential cross section dsigma/dp_T^gamma, where p_T^gamma is the momentum of the photon in the plane transverse to the beamline. The results obtained are consistent with the standard model predictions from next-to-leading order calculations. We use the transverse momentum spectrum of the photon to place limits on anomalous ZZgamma and Zgammagamma couplin…

Measurement of Associated Production ofZBosons with Charm Quark Jets inpp¯Collisions ats=1.96  TeV

We present the first measurements of the ratios of cross sections sigma(p (p) over bar -> Z + c jet)/sigma(p (p) over bar -> Z + jet) and sigma(p (p) over bar -> Z + jet)/sigma(p (p) over bar -> Z + b jet) for the associated production of a Z boson with at least one charm or bottom quark jet. Jets have transverse momentum p(T)(jet) > 20 GeV and pseudorapidity vertical bar eta(jet)vertical bar collisions collected with the D0 detector at the Fermilab Tevatron Collider at root s = 1.96 TeV. The measurements show significant deviations from perturbative QCD calculations and predictions from various event generators.

Tevatron Combination of Single-Top-Quark Cross Sections and Determination of the Magnitude of the Cabibbo-Kobayashi-Maskawa Matrix Element Vtb

et al.

Measurement of the Ratio ofB+andB0Meson Lifetimes

The ratio of the B+ and B-0 meson lifetimes was measured using data collected in 2002-2004 by the D0 experiment in Run II of the Fermilab Tevatron Collider. These mesons were reconstructed in BRμ(+)ν D*-X decays, which are dominated by B-0 and BRμ(+)ν(D) over bar X-0 decays, which are dominated by B+. The ratio of lifetimes is measured to be τ(+)/τ(0)=1.080P 0.016(stat)P 0.014(syst).

Measurement of the pp¯→W+b+X production cross section at s=1.96 TeV

We present a measurement of the cross section for $W$ boson production in association with at least one {$b$-quark} jet in proton-antiproton collisions. The measurement is made using data corresponding to an integrated luminosity of 6.1\ifb recorded with the D0 detector at the Fermilab Tevatron \ppbar Collider at $\sqrt{s}=1.96$ TeV. We measure an inclusive cross section of {$\sigma(W \sim(\to\mu\nu) + b + X) = 1.04 \pm 0.05\thinspace$(stat.) $\pm 0.12 \thinspace$(syst.) pb} and $\sigma(W (\to e\nu) + b + X) = 1.00$ \pm 0.04 \thinspace$(stat.) $\pm 0.12 \thinspace$(syst.) pb in the phase space defined by $p_T^\nu > 25$ GeV, $p_T^{\text{$b$-jet}}>20$ GeV, $|\eta^{\text{$b$-jet}}| 20$ GeV and…

Evidence for Simultaneous Production ofJ/ψandϒMesons

We report evidence for the simultaneous production of $J/\psi$ and $\Upsilon$ mesons in 8.1 fb$^{-1}$ of data collected at $\sqrt{s}=$1.96 TeV by the D0 experiment at the Fermilab $p \bar p$ Tevatron Collider. Events with these characteristics are expected to be produced predominantly by gluon-gluon interactions. In this analysis, we extract the effective cross section characterizing the initial parton spatial distribution, $\sigma_{eff}=2.2\pm 0.7\mbox{(stat)} \pm 0.9 \mbox{(syst)} ~\mbox{mb}$.

Measurement of the Effective Weak Mixing Angle in pp¯→Z/γ*→ℓ+ℓ− Events

We present a measurement of the effective weak mixing angle parameter sin(2)theta(l)(eff) in p (p) over bar -> Z/gamma* -> mu(+)mu(-) events at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron Collider and corresponding to 8.6 fb(-1) of integrated luminosity. The measured value of sin(2)theta(l)(eff)[mu mu] = 0.23016 +/- 0.00064 is further combined with the result from the D0 measurement in p (p) over bar -> Z/gamma* -> e(+)e(-) events, resulting in sin(2)theta(l)(eff)[comb] = 0.23095 +/- 0.00040. This combined result is the most precise measurement from a single experiment at a hadron collider and is the most precise determination using the couplin…

tt¯production cross section inpp¯collisions ats=1.8TeV

Measurement of the top quark pair production cross section in thelepton+jetschannel in proton-antiproton collisions ats=1.96  TeV

We present a measurement of the inclusive top quark pair production cross section in \ppbar collisions at (\sqrt{s}=1.96) TeV utilizing data corresponding to an integrated luminosity of \lumi\ collected with the D0 detector at the Fermilab Tevatron Collider. We consider final states containing one high-$p_{T}$ isolated electron or muon and at least two jets, and we perform three analyses: one exploiting specific kinematic features of \ttbar events, the second using $b$-jet identification, and the third using both techniques to separate \ttbar\ signal from background. In the third case, we determine simultaneously the $t\bar{t}$ cross section and the ratio of the production rates of $W$+heav…

Measurement of the Semileptonic Branching Ratio ofBs0to an Orbitally ExcitedDs**State:Br(Bs0→Ds1−(2536)μ+νX)

In a data sample of approximately 1.3 fb-1 collected with the D0 detector between 2002 and 2006, the orbitally excited charm state D_s1(2536) has been observed with a measured mass of 2535.7 +/- 0.6 (stat) +/- 0.5 (syst) MeV via the decay mode B0_s -> D_s1(2536) mu nu X. A first measurement is made of the branching ratio product Br(b(bar) -> D_s1(2536) mu nu X).Br(D_s1(2536)->D* K0_S). Assuming that D_s1(2536) production in semileptonic decay is entirely from B0_s, an extraction of the semileptonic branching ratio Br(B0_s -> D_s1(2536) mu nu X) is made.

Determination of the strong coupling constant from the inclusive jet cross section inpp¯collisions ats=1.96  TeV

We determine the strong coupling constant alpha(s) and its energy dependence from the p(T) dependence of the inclusive jet cross section in pp collisions at s=1.96 TeV. The strong coupling constant is determined over the transverse momentum range 50 < p(T)< 145 GeV. Using perturbative QCD calculations to order O(alpha(3)(s)) combined with O(alpha(4)(s)) contributions from threshold corrections, we obtain alpha(s)(M-Z)=0.1161(-0.0048)(+0.0041). This is the most precise result obtained at a hadron-hadron collider.

Measurement of Leptonic Asymmetries and Top Quark Polarization in ttbar Production

We present measurements of lepton (l) angular distributions in ttbar -&gt; W+ b W- b -&gt; l+ nu b l- nubar bbar decays produced in ppbar collisions at a center-of-mass energy of sqrt(s)=1.96TeV, where l is an electron or muon. Using data corresponding to an integrated luminosity of 5.4fb^-1, collected with the D0 detector at the Fermilab Collider, we find that the angular distributions of l- relative to anti-protons and l+ relative to protons are in agreement with each other. Combining the two distributions and correcting for detector acceptance we obtain the forward-backward asymmetry A^l_FB = (5.8 +- 5.1(stat) +- 1.3(syst))%, compared to the standard model prediction of A^l_FB (predicted…

A measurement of the mean lifetimes of charged and neutral B-hadrons

The decays of B-hadrons have been reconstructed using the charged particles recorded in the DELPHI silicon microstrip detector. The sum of the charges of the secondaries determines the charge of the B-hadron parent. Some 232 114 multihadronic Z0 decays recorded during the 1991 run of LEP at centre-of-mass energies between 88.2 GeV and 94.2 GeV yield 253 B-hadron candidates with well-measured charge. From these the mean lifetimes of neutral and charged B-hadrons are found to be 1.44 +/- 0.21(stat.) +/- 0.14(syst.) ps and 1.56 +/- 0.19(stat.) +/- 0.13(syst.) ps respectively. The ratio of their lifetimes is 1.09(-0.23)+0.28 (Stat.) +/- 0.11 (syst.). Under some assumptions on the abundance and …

Search for pair production of second generation scalar leptoquarks in pp¯ collisions at s=1.96 TeV

We report on a search for the pair production of second generation scalar leptoquarks (LQ_2) in ppbar collisions at the center-of-mass energy sqrt(s) = 1.96 TeV, using data corresponding to an integrated luminosity of 294 +- 19 pb^-1 recorded with the D0 detector. No evidence for a leptoquark signal in the LQ_2 LQ_2 -> muq muq channel has been observed, and upper bounds on the product of cross section times branching fraction were set. This yields lower mass limits of m(LQ_2) > 247 GeV for beta = Br(LQ_2->muq) = 1 and m(LQ_2) > 182 GeV for beta = 1/2. Combining these limits with previous D0 results, the lower limits on the mass of a second generation scalar leptoquark are m(LQ_2) > 251 GeV …

Forward-backward asymmetry in top quark-antiquark production

Made available in DSpace on 2022-04-29T02:17:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-12-12 We present a measurement of forward-backward asymmetry in top quark-antiquark production in proton-antiproton collisions in the final state containing a lepton and at least four jets. Using a data set corresponding to an integrated luminosity of 5.4fb -1, collected by the D0 experiment at the Fermilab Tevatron Collider, we measure the tt̄ forward-backward asymmetry to be (9.2±3.7)% at the reconstruction level. When corrected for detector acceptance and resolution, the asymmetry is found to be (19.6±6.5)%. We also measure a corrected asymmetry based on the lepton from a top quark deca…

Measurement of the Z$^0$ branching fraction to b quark pairs using the boosted sphericity product

Abstract From a sample of about 120 000 hadronic Z 0 decays, using a technique based on a separation of the different event categories in the boosted sphericity product, the fraction of b b decays has been measured to be 0.219 ± 0.014 (stat)± 0.019 (syst). Using the DELPHI determination of the hadronic Z 0 width, this corresponds to a partial width τ b b = 378 ± 42 MeV (in good agreement with the standard model prediction of ∼-380 MeV). Combining this measurement with the determinations based on events with high p t leptons gives an estimate for the branching ratio of b into leptons at LEP of (11.2 ± 1.2)%, consistent with previous determinations.

Combination of CDF and D0 measurements of the W boson helicity in top quark decays

Aaltonen, T. et al.

Precision Measurement of the RatioB(t→Wb)/B(t→Wq)and Extraction ofVtb

We present a measurement of the ratio of top quark branching fractions R = B(t -> Wb)/B(t -> Wq), where q can be a d, s or b quark, in the lepton+jets and dilepton ttbar final states. The measurement uses data from 5.4 fb-1 of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider. We measure R = 0.90 +/- 0.04, and we extract the CKM matrix element |Vtb| as |Vtb| = 0.95 +/- 0.02, assuming unitarity of the 3x3 CKM matrix.

Measurement of the forward-backward asymmetry ofΛandΛ¯production inpp¯collisions

We study $\Lambda$ and $\bar{\Lambda}$ production asymmetries in $p \bar{p} \rightarrow \Lambda (\bar{\Lambda}) X$, $p \bar{p} \rightarrow J/\psi \Lambda (\bar{\Lambda}) X$, and $p \bar{p} \rightarrow \mu^\pm \Lambda (\bar{\Lambda}) X$ events recorded by the D0 detector at the Fermilab Tevatron collider at $\sqrt{s} = 1.96$ TeV. We find an excess of $\Lambda$'s ($\bar{\Lambda}$'s) produced in the proton (antiproton) direction. This forward-backward asymmetry is measured as a function of rapidity. We confirm that the $\bar{\Lambda}/\Lambda$ production ratio, measured by several experiments with various targets and a wide range of energies, is a universal function of "rapidity loss", i.e., th…

Search for excited electrons inpp¯collisions ats=1.96  TeV

We present the results of a search for the production of an excited state of the electron, e(*), in proton-antiproton collisions at root s = 1.96 TeV. The data were collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 1 fb(-1). We search for e(*) in the process p (p) over bar -> e(*)e, with the e(*) subsequently decaying to an electron plus photon. No excess above the standard model background is observed. Interpreting our data in the context of a model that describes e(*) production by four-fermion contact interactions and e(*) decay via electroweak processes, we set 95% C.L. upper limits on the production cross sect…

Search for the Standard Model Higgs Boson in thepp¯→ZH→νν¯bb¯Channel

We report a search for the standard model (SM) Higgs boson based on data collected by the D0 experiment at the Fermilab Tevatron Collider, corresponding to an integrated luminosity of 260 pb^-1. We study events with missing transverse energy and two acoplanar b-jets, which provide sensitivity to the ZH production cross section in the neutrino-neutrino-b-b channel and to WH production, when the lepton from the W -> lepton+neutrino decay is undetected. The data are consistent with the SM background expectation, and we set 95% C.L. upper limits on sigma(p p-bar -> ZH/WH) x B(H -> b b-bar) from 3.4/8.3 to 2.5/6.3 pb, for Higgs masses between 105 and 135 GeV.

Search for squark production in events with jets, hadronically decaying tau leptons and missing transverse energy at s=1.96 TeV

A search for supersymmetric partners of quarks is performed in the topology of multijet events accompanied by at least one tau lepton decaying hadronically and large missing transverse energy. Approximately 1 fb(-1) of p (p) over bar collision data from the Fermilab Tevatron Collider at a center of mass energy of 1.96 TeV recorded by the D detector is analyzed. Results are combined with the previously published DO inclusive search for squarks and gluinos. No evidence of physics beyond the Standard Model is found and lower limits on the squark mass up to 410 GeV are derived in the framework of minimal supergravity with tan beta = 15, A(0) = -2m(0) and mu < 0, in the region where decays to ta…

Search for Production of Single Top Quarks ViatcgandtugFlavor-Changing-Neutral-Current Couplings

We search for the production of single top quarks via flavor-changing neutral current couplings of a gluon to the top quark and a charm ($c$) or up ($u$) quark. We analyze 230 pb$^{-1}$ of lepton + jets data from $\ppbar$ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters $\kappacLambda$ and $\kappauLambda$, where $\kappag$ define the strength of $tcg$ and $tug$ couplings, and $\Lambda$ defines the scale of new physics. The limits at 95% C.L. are: $\kappacLambda < 0.15 \rm TeV^{-1}$ and $\kappauLam…

Searches for heavy neutrinos from Z decays

We have searched for possible fourth family heavy neutrinos, pair produced in Z0 decays, in a sample of about 112 000 hadronic Z0 final states collected with the DELPHI detector. For all mixing matrix elements we exclude a new Dirac neutrino lighter than 44.5 GeV at a 95% confidence level, if the neutrino couples to the electron or muon family, and lighter than 44.0 GeV, if the neutrino couples to the tau family. Depending on the values of the mixing element and to which lepton family the neutrino couples, we obtain mass limits up to 46.2 GeV. For all mixing matrix elements we exclude a new Majorana neutrino lighter than 39.0 GeV, if it couples to the electron or the muon family, and lighte…

Search for squarks and gluinos in events with jets and missing transverse energy in pp¯ collisions at s=1.96 TeV

Abstract The results of a search for squarks and gluinos using data from p p ¯ collisions recorded at a center-of-mass energy of 1.96 TeV by the DO detector at the Fermilab Tevatron Collider are reported. The topologies analyzed consist of acoplanar-jet and multijet events with large missing transverse energy. No evidence for the production of squarks or gluinos was found in a data sample of 310 pb−1. Lower limits of 325 and 241 GeV were derived at the 95% C.L. on the squark and gluino masses, respectively, within the framework of minimal supergravity with tan β = 3 , A 0 = 0 , and μ 0 .

Search for Leptoquark Pairs Decaying intoνν+jetsinpp¯Collisions ats=1.8TeV

We present the results of a search for leptoquark (LQ) pairs in (85.2+/-3.7) pb(-1) of pp* collider data collected by the D0 experiment at the Fermilab Tevatron. We observe no evidence for leptoquark production and set a limit on sigma(pp*-->LQLQ-->nunu+jets) as a function of the mass of the leptoquark (m(LQ)). Assuming the decay LQ-->nuq, we exclude scalar leptoquarks for m(LQ) < 98 GeV/c(2), and vector leptoquarks for m(LQ) < 200 GeV/c(2) and coupling which produces the minimum cross section, at a 95% confidence level.

Search for Higgs boson production in oppositely charged dilepton and missing energy events inpp¯collisions ats=1.96  TeV

We present a search for the standard model Higgs boson using events with two oppositely charged leptons and large missing transverse energy as expected in $H\rightarrow WW$ decays. The events are selected from data corresponding to 8.6 \ifb\ of integrated luminosity in $p \bar{p}$ collisions at $\sqrt{s}=1.96$ TeV collected with the D0 detector at the Fermilab Tevatron Collider. No significant excess above the standard model background expectation in the Higgs boson mass range this search is sensitive to is observed, and upper limits on the Higgs boson production cross section are derived.

Search for first generation leptoquark pair production in the electron + missing energy + jets final state

We present a search for the pair production of first generation scalar leptoquarks (LQ) in data corresponding to an integrated luminosity of 5.4 fb$^{-1}$ collected with the D0 detector at the Fermilab Tevatron Collider in ppbar collisions at $\sqrt{s}=1.96$ TeV. In the channel $LQ \bar{LQ} \rightarrow e\nu_e qq'$, where q, q' are u or d quarks, no significant excess of data over background is observed, and we set a 95% C.L. lower limit of 326 GeV on the leptoquark mass, assuming equal probabilities of leptoquark decays to eq and $\nu_e q'$.

Search for the Standard Model Higgs Boson in AssociatedWHProduction in9.7  fb−1ofpp¯Collisions with the D0 Detector

We present a search for the standard model Higgs boson in final states with a charged lepton (electron or muon), missing transverse energy, and two or three jets, at least one of which is identified as a b-quark jet. The search is primarily sensitive to WH→lνbb production and uses data corresponding to 9.7 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron pp Collider at √s = 1.96 TeV. We observe agreement between the data and the expected background. For a Higgs boson mass of 125 GeV, we set a 95% C.L. upper limit on the production of a standard model Higgs boson of 5.2 × σ(SM), where σ(SM) is the standard model Higgs boson production cross section, whi…

Tevatron constraints on models of the Higgs boson with exotic spin and parity using decays to bottom-antibottom quark pairs.

et al.

Measurement of the tt¯ production cross section and top quark mass extraction using dilepton events in pp¯ collisions

We present a measurement of the top quark pair production cross section in p (p) over bar collisions at root s = 1.96 TeV using approximately 1 fb(-1) collected with the DO detector. We consider decay channels containing two high p(T) charged leptons where one lepton is identified as an electron or a muon while the other lepton can be an electron, a muon or a hadronically decaying tau lepton. For a mass of the top quark of 170 GeV, the measured cross section is 7.5(-1.0)(+1.0)(stat)(-0.6)(+0.7)(syst)(-0.5)(+0.6)(lumi) pb. Using l tau events only, we measure: sigma(t (t) over bar) x B(t (t) over bar -> l tau b (b) over bar) = 0.13(-0.08)(+0.09)(stat)(-0.06)(+0.06)(syst)(-0.02)(+0.02)(lumi) p…

Jet energy scale determination in the D0 experiment

The calibration of jet energy measured in the \DZero detector is presented, based on ppbar collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. Jet energies are measured using a sampling calorimeter composed of uranium and liquid argon as the passive and active media, respectively. This paper describes the energy calibration of jets performed with photon+jet, Z+jet and dijet{} events, with jet transverse momentum pT &gt; 6 GeV and pseudorapidity range |eta| &lt; 3.6. The corrections are measured separately for data and simulation, achieving a precision of 1.4%-1.8% for jets in the central part of the calorimeter and up to 3.5% for the jets with pseudorapidity…

Search for ResonantWWandWZProduction inpp¯Collisions ats=1.96  TeV

We search for resonant WW or WZ production using up to 5.4 fb-1 of integrated luminosity collected by the D0 experiment in Run II of the Fermilab Tevatron Collider. The data are consistent with the standard model background expectation, and we set limits on a resonance mass using the sequential standard model (SSM) W' boson and the Randall-Sundrum model graviton G as benchmarks. We exclude an SSM W' boson in the mass range 180 - 690 GeV and a Randall-Sundrum graviton in the range 300 - 754 GeV at 95% CL.

Double parton interactions inγ+3jet events inpp¯collisions ats=1.96  TeV

We have used a sample of photon+3 jets events collected by the D0 experiment with an integrated luminosity of about 1 fb^-1 to determine the fraction of events with double parton scattering (f_DP) in a single ppbar collision at sqrt{s}=1.96 TeV. The DP fraction and effective cross section (sigma_eff), a process-independent scale parameter related to the parton density inside the nucleon, are measured in three intervals of the second (ordered in pT) jet transverse momentum pT_jet2 within the range 15 < pT_jet2 < 30 GeV. In this range, f_DP varies between 0.23 < f_DP < 0.47, while sigma_eff has the average value sigma_eff_ave = 16.4 +- 0.3(stat) +- 2.3(syst) mb.

Evidence for production of single top quarks

We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron ppbar collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top quark partner that is always produced from strong coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top quark production has been searched for in ever larger datasets. In this analysis, we select events from a 0.9 fb-1 dataset that have an electron or muon and missing transverse energy from the decay of a W boson from the top quark decay, and two, three, …

Search for Higgs bosons of the minimal supersymmetric standard model in pp¯ collisions at s=1.96 TeV

We report results from searches for neutral Higgs bosons produced in p-pbar collisions recorded by the Dzero experiment at the Fermilab Tevatron Collider. We study the production of inclusive neutral Higgs boson in the tautau final state and in association with a b quark in the btautau and bbb final states. These results are combined to improve the sensitivity to the production of neutral Higgs bosons in the context of the minimal supersymmetric standard model (MSSM). The data are found to be consistent with expectation from background processes. Upper limits on MSSM Higgs boson production are set for Higgs boson masses ranging from 90 to 300 GeV. We exclude tanBeta>20-30 for Higgs boson ma…

Study of double parton interactions indiphoton+dijetevents inpp¯collisions ats=1.96  TeV

We use a sample of diphoton+dijet events to measure the effective cross section of double parton interactions, which characterizes the area containing the interacting partons in proton-antiproton collisions, and find it to be σeff=19.3±1.4(stat)±7.8(syst) mb. The sample was collected by the D0 detector at the Fermilab Tevatron collider in $$p\bar{p}$$ collisions at $$\sqrt{s} = 1.96$$ TeV and corresponds to an integrated luminosity of 8.7 fb-1.

Measurement of thepp¯→WZ+Xcross section ats=1.96  TeVand limits onWWZtrilinear gauge couplings

We present measurements of the process p (P) over bar -> WZ + X -> l 'nu(l ')l (l) over bar at root s = 1:96 TeV,where l and l ' are electrons or muons. Using 1 fb(-1) of data from the D0 experiment, we observe 13 candidates with an expected background of 4.5 +/- 0.6 events and measure a cross section sigma(WZ) = 2.7(-1.3)(+1.7) pb. From the number of observed events and the Z boson transverse momentum distribution, we limit the trilinear WWZ gauge couplings to -0: 17 <= lambda(Z) <= 0.21 (Delta k(Z) <= 0.29(lambda(Z) = 0) at the 95% C.L. for a form factor scale Lambda = 2 TeV. Further, assuming that Delta g(1)(Z) = Delta k(Z), we find -0.12 <= Delta k(Z) <= 0.29(lambda(Z) = 0) at the 95% C…

Measurement of theWBoson Production Charge Asymmetry inpp¯→W+X→eν+XEvents ats=1.96  TeV

We present a measurement of the W boson production charge asymmetry in p (p) over bar -> W + X -> ev + X events at a center of mass energy of 1.96 TeV, using 9.7 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The neutrino longitudinal momentum is determined by using a neutrino weighting method, and the asymmetry is measured as a function of the W boson rapidity. The measurement extends over wider electron pseudorapidity region than previous results and is the most precise to date, allowing for precise determination of proton parton distribution functions in global fits.

Multiple jet production at low transverse energies inpp¯collisions ats=1.8TeV

We present data on multiple production of jets with transverse energies near 20 GeV in p (p) over bar collisions at roots=1.8 TeV. QCD calculations in the parton-shower approximation of PYTHIA and HERWIG and the next-to-leading order approximation of JETRAD are compared to the data for one, two, three, and four jet inclusive production. Transverse energy spectra and multiple jet angular and summed transverse-energy distributions are adequately described by the shower approximation while next-to-leading order calculations describe the data poorly.

Measurement of thepp¯→Wγ+Xcross section ats=1.96 TeV andWWγanomalous coupling limits

The WWgamma triple gauge boson coupling parameters are studied using p-pbar -> l nu gamma + X (l = e,mu) events at sqrt(s) = 1.96 TeV. The data were collected with the DO detector from an integrated luminosity of 162 pb^{-1} delivered by the Fermilab Tevatron Collider. The cross section times branching fraction for p-pbar -> W(gamma) + X -> l nu gamma + X with E_T^{gamma} > 8 GeV and Delta R_{l gamma} > 0.7 is 14.8 +/- 1.6 (stat) +/- 1.0 (syst) +/- 1.0 (lum) pb. The one-dimensional 95% confidence level limits on anomalous couplings are -0.88 < Delta kappa_{gamma} < 0.96 and -0.20 < lambda_{gamma} < 0.20.

Observation and Properties of theX(3872)Decaying toJ/ψπ+π−inpp¯Collisions ats=1.96  TeV

We report the observation of the X(3872) in the J/psipi(+)pi(-) channel, with J/psi decaying to mu(+)mu(-), in p (p) over bar collisions at roots=1.96 TeV. Using approximately 230 pb(-1) of data collected with the Run II D0 detector, we observe 522+/-100 X(3872) candidates. The mass difference between the X(3872) state and the J/psi is measured to be 774.9+/-3.1(stat)+/-3.0(syst) MeV/c(2). We have investigated the production and decay characteristics of the X(3872) and find them to be similar to those of the psi(2S) state.

A measurement of the \(\tau\) leptonic branching fractions

Abstract: A sample of 25000 Z(0) --> tau(-)tau(+) events collected by the DELPHI experiment at LEP in 1991 and 1992 is used to measure the leptonic branching fractions of the tau lepton. The results are B(tau --> e nu) = (17.51+/-0.39)% and B(tau --> mu nu) = (17.02+/-0.31)%. The ratio of the muon and electron couplings to the weak charged current is measured to be g(mu)/g(e) = 1.000+/-0.013, satisfying e-mu universality. The average leptonic branching fraction corrected to the value for a massless lepton, assuming e-mu universality, is found to be B(tau --> l nu) = (17.50+/-0.25)%.

Measurement of theWWProduction Cross Section with Dilepton Final States inpp¯Collisions ats=1.96  TeVand Limits on Anomalous Trilinear Gauge Couplings

We provide the most precise measurement of the WW production cross section in p-pbar collisions to date at a center of mass energy of 1.96 TeV, and set limits on the associated trilinear gauge couplings. The WW->lvl'v (l,l'=e,mu) decay channels are analyzed in 1 fb^(-1) of data collected by the D0 detector at the Fermilab Tevatron Collider. The measured cross section is sigma(p-pbar -> WW) = 11.5 +/- 2.1 (stat + syst) +/- 0.7 (lumi) pb. One- and two-dimensional 95% C.L. limits on trilinear gauge couplings are provided.

Search for scalar bottom quarks and third-generation leptoquarks in pp¯ collisions at s=1.96 TeV

We report the results of a search for pair production of scalar bottom quarks ((b) over bar (1)) and scalar third-generation leptoquarks (LQ(3)) in 5.2 fb(-1) of p (p) over bar collisions at the D0 experiment of the Fermilab Tevatron Collider. Scalar bottom quarks are assumed to decay to a neutralino ((chi) over bar (1)(0)) and a b quark, and we set 95% C.L. lower limits on their production in the (m((b) over bar1), m((chi) over bar 10)) mass plane such as m((b) over bar1) > 247 GeV for m( 10) = 0 and m((chi) over bar 10) > 110 GeV for 160 m(<(b) over bar1) < 200 GeV. The leptoquarks are assumed to decay to a tau neutrino and a b quark, and we set a 95% C.L. lower limit of 247 GeV on the ma…

Measurement of angular correlations of jets at s=1.96 TeV and determination of the strong coupling at high momentum transfers

We present a measurement of the average value of a new observable at hadron colliders that is sensitive to QCD dynamics and to the strong coupling constant, while being only weakly sensitive to parton distribution functions. The observable measures the angular correlations of jets and is defined as the number of neighboring jets above a given transverse momentum threshold which accompany a given jet within a given distance Delta-R in the plane of rapidity and azimuthal angle. The ensemble average over all jets in an inclusive jet sample is measured and the results are presented as a function of transverse momentum of the inclusive jets, in different regions of Delta-R and for different tran…

Search for Charged Higgs Bosons Decaying into Top and Bottom Quarks in pp Collisions

Made available in DSpace on 2022-04-28T20:54:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-05-14 We describe a search for production of a charged Higgs boson, qq̄′→H+, reconstructed in the tb̄ final state in the mass range 180≤MH+≤300GeV. The search was undertaken at the Fermilab Tevatron collider with a center-of-mass energy s=1.96TeV and uses 0.9fb-1 of data collected with the D0 detector. We find no evidence for charged Higgs boson production and set upper limits on the production cross section in the types I, II, and III two-Higgs-doublet models (2HDMs). An excluded region in the (MH+, tanβ) plane for type I 2HDM is presented. © 2009 The American Physical Society. Universida…

Search for a Resonance Decaying intoWZBoson Pairs inpp¯Collisions

We present the first search for an electrically charged resonance W' decaying to a WZ boson pair using 4.1 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron p (p) over bar collider. The WZ pairs are reconstructed through their decays into three charged leptons (l = e, mu). A total of 9 data events is observed in good agreement with the background prediction. We set 95% C.L. limits on the W'WZ coupling and on the W' production cross section multiplied by the branching fractions. We also exclude W' masses between 188 and 520 GeV within a simple extension of the standard model and set the most restrictive limits to date on low-scale technicolor models.

Direct Observation of the StrangebBaryonΞb−

We report the first direct observation of the strange b baryon Xi(b)- (Xi(b)+). We reconstruct the decay Xi(b)- -->J/psiXi-, with J/psi-->mu+mu-, and Xi--->Lambdapi--->ppi-pi- in pp collisions at square root of s =1.96 TeV. Using 1.3 fb(-1) of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat)(-0.4)(+1.9)(syst) Xi(b)- candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)-->J/psiLambda, we measure the relative rate sigma(Xi(b-) x B(Xi)b})- -->J/psiXi-)/sigma(Lambda(b)) x B(Lambda(b)-->J/psi…

Search for the Scalar Top Quark inpp¯Collisions ats=1.8TeV

We have performed a search for scalar top quark (stop) pair production in the inclusive electron-muon-missing transverse energy final state, using a sample of p (p) over bar events corresponding to 108.3 pb (-1) of data collected with the D0 detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the sneutrino is the lightest supersymmetric particle. For the dominant decays of the lightest stop, (t) over tilde-->b (χ) over tilde (+)(1) and (t) over tilde-->bl (ν) over tilde , no evidence for signal is found. We derive cross-section limits as a function of stop ((t) over tilde), chargino ((χ) over tilde (+)(1)), and sneutrino ((ν) …

Measurement of the anomalous like-sign dimuon charge asymmetry with9  fb−1ofpp¯collisions

We present an updated measurement of the anomalous like-sign dimuon charge asymmetry A(sl)(b) for semileptonic b-hadron decays in 9.0 fb(-1) of p (p) over bar collisions recorded with the D0 detector at a center-of-mass energy of root s = 1.96 TeV at the Fermilab Tevatron collider. We obtain A(sl)(b) = (-0.787 +/- 0.172(stat) +/- 0.093(syst)%. This result differs by 3.9 standard deviations from the prediction of the standard model and provides evidence for anomalously large CP violation in semileptonic neutral B decay. The dependence of the asymmetry on the muon impact parameter is consistent with the hypothesis that it originates from semileptonic b-hadron decays.

Search for the Standard Model Higgs Boson inZH→ℓ+ℓ−bb¯Production with the D0 Detector in9.7  fb−1ofpp¯Collisions ats=1.96  TeV

We acknowledge support from the DOE and NSF (USA); CEA and CNRS/IN2P3 (France); FASI, Rosatom, and RFBR (Russia); CNPq, FAPERJ, FAPESP, and FUNDUNESP (Brazil); DAE and DST (India); Colciencias (Colombia); CONACyT (Mexico); KRF and KOSEF (Korea); CONICET and UBACyT (Argentina); FOM (Netherlands); STFC and the Royal Society (United Kingdom); MSMT and GACR (Czech Republic); CRC Program and NSERC (Canada); BMBF and DFG (Germany); SFI (Ireland); The Swedish Research Council (Sweden); and CAS and CNSF (China).

Measurement of theWZ→ℓνℓℓcross section and limits on anomalous triple gauge couplings inpp¯collisions ats=1.96TeV

We present a new measurement of the WZ -> lvll (l = e, mu) cross section and limits on anomalous triple gauge couplings. Using 4.1 fb(-1) of integrated luminosity of p (p) over bar collisions at root s = 1.96 TeV, we observe 34 WZ candidate events with an estimated background of 6.0 +/- 0.4 events. We measure the WZ production cross section to be 3.89(-0.90)(+1.07) pb, in good agreement with the standard model prediction. We find no evidence for anomalous WWZ couplings and set 95% C.L. limits on the coupling parameters, -0.077 < lambda(z) < 0.093 and -0.029 < Delta kappa(z) < 0.080 in the HISZ parameterization for a Lambda = 2 TeV form factor scale. These are the best limits to date obtaine…

PRODUCTION-RATE AND DECAY LIFETIME MEASUREMENTS OF B(S)0 MESONS AT LEP USING D(S) AND PHI MESONS

The study of the properties of inclusive production of Ds mesons and of events in which a φ{symbol} and a muon are present in the same jet provides two independent measurements of the probability, fs w, for a heavy quark to hadronize into a strange B or D meson. The data sample analysed corresponds to 243,000 hadronic Z0 decays. The combined value of these measurements is fs w=0.19±0.06±0.08. From the flight distance distributions of Ds and of (φ{symbol}-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for the Bs 0 meson lifetime. Combining these measurements with a previous result based on the study of Ds-μ ev…

Search for pair production of the scalar top quark in muon+tau final states

We present a search for the pair production of scalar top quarks ($\tilde{t}_{1}$), the lightest supersymmetric partners of the top quarks, in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV, using data corresponding to an integrated luminosity of {7.3 $fb^{-1}$} collected with the \dzero experiment at the Fermilab Tevatron Collider. Each scalar top quark is assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tilde{\nu}$). We investigate final states arising from $\tilde{t}_{1} \bar{\tilde{t}_{1}} \rightarrow b\bar{b}\mu\tau \tilde{\nu} \tilde{\nu}$ and $\tilde{t}_{1} \bar{\tilde{t}_{1}} \rightarrow b\bar{b}\tau\tau \tilde{\nu} \tilde{\nu}$. With no si…

Search for a Higgs boson in diphoton final states with the D0 detector in9.6  fb−1ofpp¯collisions ats=1.96  TeV

We present a search for a Higgs boson decaying into a pair of photons based on 9.6 fb-1 of p-pbar collisions at sqrt(s)=1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The search employs multivariate techniques to discriminate signal from the non-resonant background and is separately optimized for a standard model and a fermiophobic Higgs boson. No significant excess of data above the background prediction is observed and upper limits on the product of the cross section and branching fraction are derived at the 95% confidence level as a function of Higgs boson mass. For a standard model Higgs boson with mass of 125 GeV, the observed (expected) upper limits are a f…

Measurement of the Shape of the Boson-Transverse Momentum Distribution inpp¯→Z/γ*→e+e−+XEvents Produced ats=1.96  TeV

We present a measurement of the shape of the Z/gamma* boson transverse momentum (q(T)) distribution in p (p) over bar -> Z/gamma(*)-> e(+)e(-)+X events at a center-of-mass energy of 1.96 TeV using 0.98 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron collider. The data are found to be consistent with the resummation prediction at low q(T), but above the perturbative QCD calculation in the region of q(T)> 30 GeV/c. Using events with q(T)< 30 GeV/c, we extract the value of g(2), one of the nonperturbative parameters for the resummation calculation. Data at large boson rapidity y are compared with the prediction of resummation and with alternative models that employ a res…

Search for Pair Production of Doubly Charged Higgs Bosons in theH++H--→μ+μ+μ−μ−Final State

We report the results of a search for pair production of doubly-charged Higgs bosons via ppbar to H^{++}H^{--}X to mu^+mu^+mu^-mu^-X at sqrt{s} = 1.96 TeV. We use a dataset corresponding to an integrated luminosity of 1.1 fb^{-1} collected from 2002 to 2006 by the D0 detector at the Fermilab Tevatron Collider. In the absence of an excess above the standard model background, lower mass limits of M(H^{pmpm}_L) > 150 GeV/c^2 and M(H^{pmpm}_R) > 127 GeV/c^2 at 95% C.L. are set, respectively, for left-handed and right-handed doubly-charged Higgs bosons assuming a 100% branching ratio into muons.

Search for Decay of a Fermiophobic Higgs Bosonhf→γγwith the D0 Detector ats=1.96  TeV

We report the results of a search for a narrow resonance decaying into two photons in 1.1 fb(-1) of data collected by the D0 experiment at the Fermilab Tevatron Collider during the period 2002-2006. We find no evidence for such a resonance and set a lower limit on the mass of a fermiophobic Higgs boson of m(hf) > 100 GeV at the 95% C.L. This exclusion limit exceeds those obtained in previous searches at the Fermilab Tevatron and covers a significant region of the parameter space B(h(f) -> gamma gamma) vs m(hf) which was not accessible at the CERN Large Electron-Positron Collider.

A measurement of αs from the scaling violation in e+e- annihilation

The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from $\zz$ decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at energies between 14 GeV and 91 GeV. A large scaling violation is observed, which is used to extract the strong coupling constant from a fit using a numerical integration of the second order DGLAP evolution equations. The result is \begin{displaymath} \alpha_s(M_Z) = 0.124^{+0.006}_{-0.007}(exp)\pm 0.009 (theory) \end{displaymath} where the first error represents the experimental uncertainty and the second error is due to the factorization a…

Energy dependence of event shapes and of $\alpha_s$ at LEP 2

Infrared and collinear safe event shape distributions and their mean values are determined using the data taken at five different centre of mass energies above M-Z with the DELPHI detector at LEP. From the event shapes, the strong coupling alpha(s) is extracted in O(alpha(s)(2)), NLLA and a combined scheme using hadronisation corrections evaluated with fragmentation model generators as well as using an analytical power ansatz. Comparing these measurements to those obtained at M-Z, the energy dependence (running) of alpha(s) is accessible. The logarithmic energy slope of the inverse strong coupling is measured to be d alpha(s)(-1)/d log(E-cm) = 1.39 +/- 0.34 (stat) +/- 0.17(syst), in good ag…

Muon reconstruction and identification with the Run II D0 detector

We present an overview of the muon reconstruction and identification methods employed by the D0 Collaboration to analyze the Run II (2001-2011) ppbar data of the Fermilab Tevatron collider at sqrt s = 1.96 TeV. We discuss the performance of these methods, how it is measured using D0 data, and how it is properly modeled by the D0 simulation program. In its pseudorapidity acceptance, eta&lt; 2, the muon system identifies high-pT muons (pT&gt;10 GeV) with efficiencies ranging from 72% to 89%. Muons tracks are reconstructed in the D0 central tracking system with efficiencies ranging from 85% to 92% and with a typical relative momentum resolution of 10% for pT = 40 GeV. Isolation criteria reject…

Production ofWZEvents inpp¯Collisions ats=1.96  TeVand Limits on AnomalousWWZCouplings

We present results from a search for WZ production with subsequent decay to l nu l'(l) over bar'(l and l' = e or mu) using 0.30 fb(-1) of data collected by the D0 experiment between 2002 and 2004 at the Fermilab Tevatron. Three events with WZ decay characteristics are observed. With an estimated background of 0.71 +/- 0.08 events, we measure the WZ production cross section to be 4.5(-2.6)(+3.8) pb, with a 95% C.L. upper limit of 13.3 pb. The 95% C.L. limits for anomalous WWZ couplings are found to be -2.0 <Delta kappa(Z)< 2.4 for form factor scale Lambda=1 TeV, and -0.48 <lambda(Z)< 0.48 and -0.49 <Delta g(1)(Z)< 0.66 for Lambda=1.5 TeV.

Charged particle multiplicity in e^{+}e_{-}$ → q[L:q] events at 161 and 172 GeV and from the decay of the W boson

The data collected by DELPHI in 1996 have been used to measure the average charged particle multiplicities and dispersions in $q\bar{q}$ events at centre-of-mass energies of $\sqrt{s}=161$~GeV and $\sqrt{s}=172$~GeV, and the average charge multiplicity in WW events at $\sqrt{s}=172$~GeV. The multiplicities in $q\bar{q}$ events are consistent with the evolution predicted by QCD. The dispersions in the multiplicity distributions are consistent with Koba-Nielsen-Olesen (KNO) scaling. The average multiplicity of charged particles in hadronic W decays has been measured for the first time; its value, $19.23 \pm 0.74 (stat+syst)$, is consistent with that expected for an $e^+e^-$ interaction at a c…

Search for R-parity violating supersymmetry in two-muon and four-jet topologies

We present results of a search for R-parity-violating decay of the neutralino chi;01, taken as the lightest supersymmetric particle, to a muon and two jets. The decay proceeds through a lepton-number violating coupling lambda(')(2jk) (j=1,2; k=1,2,3), with R-parity conservation in all other production and decay processes. In the absence of candidate events from 77.5+/-3.9 pb(-1) of data collected by the D0 experiment at the Fermilab Tevatron in pp collisions at sqrt[s]=1.8 TeV, and with an expected background of 0.18+/-0.03+/-0.02 events, we set limits on squark and gluino masses within the framework of the minimal low-energy supergravity-supersymmetry model.

Search for new fermions ("quirks") at the Fermilab Tevatron Collider

We report results of a search for particles with anomalously high ionization in events with a high transverse energy jet and large missing transverse energy in $2.4$ fb$^{-1}$ of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron $p\bar{p}$ collider. Production of such particles (quirks) is expected in scenarios with extra QCD-like {\it SU(N)} sectors, and this study is the first dedicated search for such signatures. We find no evidence of a signal and set a lower mass limit of 107 ~GeV for the mass of a charged quirk with strong dynamics scale $\Lambda$ in the range from 10 keV to 1 MeV.

Search for Scalar Neutrino Superpartners ine+μFinal States inpp¯Collisions ats=1.96  TeV

We report a search for R-parity-violating production and decay of sneutrino particles in the e mu final state with 1.04 +/- 0.06 fb(-1) of data collected with the D-0 detector at the Fermilab Tevatron Collider in 2002-2006. Good agreement between the data and the standard model prediction is observed. With no evidence for new physics, we set limits on the R-parity-violating couplings lambda'(311) and lambda(312) as a function of the sneutrino mass.

Search forZH→ℓ+ℓ−bb¯production in9.7  fb−1ofpp¯collisions with the D0 detector

We present a search for the standard model (SM) Higgs boson produced in association with a Z boson in 9.7 fb-1 of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider at sqrt{s} = 1.96 TeV. Selected events contain one reconstructed Z -> e+e- or Z -> mu+mu- candidate and at least two jets, including at least one jet likely to contain a b quark. To validate the search procedure, we also measure the cross section for ZZ production, and find that it is consistent with the SM expectation. We set upper limits at the 95% C.L. on the product of the ZH production cross section and branching ratio B(H -> bbbar) for Higgs boson masses 90

Measurement of the forward-backward asymmetries in the production ofΞandΩbaryons inpp¯collisions

We measure the forward-backward asymmetries $A_{\rm FB}$ of charged $\Xi$ and $\Omega$ baryons produced in $p \bar{p}$ collisions recorded by the D0 detector at the Fermilab Tevatron collider at $\sqrt{s} = 1.96$ TeV as a function of the baryon rapidity $y$. We find that the asymmetries $A_{\rm FB}$ for charged $\Xi$ and $\Omega$ baryons are consistent with zero within statistical uncertainties.

Search for the standard model Higgs boson in tau lepton final states

We present a search for the standard model Higgs boson in final states with an electron or muon and a hadronically decaying tau lepton in association with zero, one, or two or more jets using data corresponding to an integrated luminosity of up to 7.3 fb^{-1} collected with the D0 detector at the Fermilab Tevatron collider. The analysis is sensitive to Higgs boson production via gluon gluon fusion, associated vector boson production, and vector boson fusion, and to Higgs boson decays to tau lepton pairs or W boson pairs. Observed (expected) limits are set on the ratio of 95% C.L. upper limits on the cross section times branching ratio, relative to those predicted by the Standard Model, of 1…

Combination oftt¯cross section measurements and constraints on the mass of the top quark and its decays into charged Higgs bosons

We combine measurements of the top quark pair production cross section in p (p) over bar collisions in the l + jets, ll, and tau l final states ( where l is an electron or muon) at a center of mass energy of root s = 1.96 TeV in 1 fb(-1) of data collected with the D0 detector. For a top quark mass of 170 GeV/c(2), we obtain sigma(t (t) over bar) = 8.18(-0.87)(+0.98) pb in agreement with the theoretical prediction. Based on predictions from higher order quantum chromodynamics, we extract a mass for the top quark from the combined t (t) over bar cross section, consistent with the world average of the top quark mass. In addition, the ratios of t (t) over bar cross sections in different final s…

Search for anomalous heavy-flavor quark production in association with W bosons.

We present a search for anomalous production of heavy-flavor quark jets in association with a W boson at the Fermilab Tevatron ppbar Collider. This search is conducted through an examination of the exclusive jet spectrum of W+jets final states in which the heavy-flavor quark content has been enhanced by requiring at least one tagged jet in an event. Jets are tagged by the combined use of two algorithms, one based on semileptonic decays of b/c hadrons, and the other on their lifetimes. We compare data in e+jets (164 pb-1) and mu+jets (145 pb-1) channels, collected with the D0 detector at sqrt{s}=1.96 TeV, to expectations from the standard model, and set upper limits on anomalous production o…

Search for third generation scalar leptoquarks decaying into tau b

We have searched for third generation leptoquarks (LQ3) using 1.05 inverse femtobarns of data collected with the D0 detector at the Fermilab Tevatron Collider operating at sqrt(s)=1.96 TeV. We set a 95% C.L. lower limit of 210 GeV on the mass of a scalar LQ3 state decaying solely to a b quark and a tau lepton.

Measurement of the forward-backward asymmetry in top quark-antiquark production inpp¯collisions using thelepton+jetschannel

We present a measurement of the forward-backward asymmetry in top quark-antiquark production using the full Tevatron Run II data set collected by the D0 experiment at Fermilab. The measurement is performed in lepton + jets final states using a new kinematic fitting algorithm for events with four or more jets and a new partial reconstruction algorithm for events with only three jets. Corrected for detector acceptance and resolution effects, the asymmetry is evaluated to be A(FB) = (10.6 +/- 3.0)%. Results are consistent with the standard model predictions which range from 5.0% to 8.8%. We also present the dependence of the asymmetry on the invariant mass of the top quark-antiquark system and…

Search for Large Extra Dimensions in theMonojet+E̸TChannel with the DØ Detector

We present a search for large extra dimensions (ED) in p (p) over bar collisions at a center-of-mass energy of 1.8 TeV using data collected by the DO detector at the Fermilab Tevatron in 1994-1996. Data corresponding to 78.8+/-3.9 pb(-1) are examined for events with large missing transverse energy, one high-p(T) jet, and no isolated muons. There is no excess observed beyond expectation from the standard model, and we place lower limits on the fundamental Planck scale of 1.0 and 0.6 TeV for 2 and 7 ED, respectively.

Measurement of trilinear gauge boson couplings fromWW+WZ→lνjjevents inpp¯collisions ats=1.96  TeV

We present a direct measurement of trilinear gauge boson couplings at gamma WW and ZWW vertices inWW and WZ events produced in p (p) over bar collisions at root s = 1:96 TeV. We consider events with one electron or muon, missing transverse energy, and at least two jets. The data were collected using the D0 detector and correspond to 1:1 fb(-1) of integrated luminosity. Considering two different relations between the couplings at the gamma WW and ZWW vertices, we measure these couplings at 68% C.L. to be kappa(gamma) = 1.07(-0.29)(+0.26) lambda = 0.00(-0.06)(+0.00), and g(1)(Z) = 1.04(-0.09)(+0.09) in a scenario respecting SU(2)(L) circle times U(1)(Y) gauge symmetry and kappa = 1.04(-0.11)(…

Search forCPviolation inBs0→μ+Ds−Xdecays inpp¯collisions ats=1.96  TeV

We have performed a search for CP violation in a sample of B-s(0) -> mu+Ds-X decays corresponding to 5 fb(-1) of proton-antiproton collisions collected by the D0 detector in Run II at the Fermilab Tevatron Collider. New physics in B-s(0) mixing could contribute a significant CP violating weak phase, which would be observed as a difference in the decay-time distribution for B-s(0) -> (B) over bar (0)(s) oscillated states versus that for (B) over bar (0)(s) -> B-s(0). A fit to the decay-time distributions of the B-s(0)/(B) over bar (0)(s) candidates yields the flavor-specific asymmetry as a(fs)(s) = [-1.7 +/- 9.1(stat)(-1.5)(+1.4)(syst) x 10(-3), which excludes CP violation due to new physics…

Limits on anomalous trilinear gauge boson couplings from WW, WZ and Wγ production in pp¯ collisions at s=1.96 TeV

We present searches for the anomalous γWW and ZWW trilinear gauge boson couplings from WW and WZ production using lepton plus dijet final states and a combination with results from Wγ, WW, and WZ production with leptonic final states. The analyzed data correspond to up to 8.6fb -1 of integrated luminosity collected by the D0 detector in pp- collisions at s=1.96TeV. We set the most stringent limits at a hadron collider to date assuming two different relations between the anomalous coupling parameters δκ γ, λ, and δg1Z for a cutoff energy scale Λ=2TeV. The combined 68% C.L. limits are -0.057lδκ γl0.154, -0.015lλl0.028, and -0.008lδg1Zl0.054 for the LEP parameterization, and -0.007lδκl0.081 an…

Measurement of the transverse spin correlation in Z → τ+ τ- decays

The measurement of the correlation between the transverse spin components of tau(+)tau(-) pairs collected during 1992 to 1994 with the DELPHI detector at LEP1 is presented. A value C-TT = 0.87 +/- 0.20 (stat.)(-0.12)(+0.10) (syst.) was obtained for the correlation parameter, in agreement with the Standard Model expectation. (C) 1997 Published by Elsevier Science B.V.

Search for anomalous Wtb couplings in single top quark production in pp¯ collisions at s=1.96 TeV

We present new direct constraints on a general $Wtb$ interaction using data corresponding to an integrated luminosity of 5.4 fb$^{-1}$ collected by the D0 detector at the Tevatron $p\bar{p}$ collider. The standard model provides a purely left-handed vector coupling at the $Wtb$ vertex, while the most general, lowest dimension Lagrangian allows right-handed vector and left- or right-handed tensor couplings as well. We obtain precise limits on these anomalous couplings by comparing the data to the expectations from different assumptions on the $Wtb$ coupling.

Measurement of the Forward-Backward Asymmetry in the Production ofB±Mesons inpp¯Collisions ats=1.96  TeV

We present a measurement of the forward-backward asymmetry in the production of B-+/- mesons, A(FB)(B-+/-) using B-+/- -> J/ Psi K-+/- decays in 10.4 fb(-1) of p (p) over bar collisions at root s = 1.96 TeV collected by the D0 experiment during Run II of the Tevatron collider. A nonzero asymmetry would indicate a preference for a particular flavor, i.e., b quark or (b) over bar antiquark, to be produced in the direction of the proton beam. We extract A(FB) (B-+/-) from a maximum likelihood fit to the difference between the numbers of forward-and backward-produced B-+/- mesons. We measure an asymmetry consistent with zero: A(FB) (B-+/-) = [-0.24 +/- 0.41 (stat) +/- 0.19 (syst)] %.

Lifetime Difference andCP-Violating Phase in theBs0System

From an analysis of the decay B-s(0)-> J/psi phi, we obtain the width difference between the light and heavy mass eigenstates Delta Gamma equivalent to(Gamma(L)-Gamma(H))=0.17 +/- 0.09(stat)+/- 0.02(syst) ps(-1) and the CP-violating phase phi(s)=-0.79 +/- 0.56(stat)(-0.01)(+0.14)(syst). Under the hypothesis of no CP violation (phi(s)equivalent to 0), we obtain 1/Gamma=tau/(B-s(0))=1.52 +/- 0.08(stat)(-0.03)(+0.01)(syst) ps and Delta Gamma=0.12(-0.10)(+0.08)(stat)+/- 0.02(syst) ps(-1). The data sample corresponds to an integrated luminosity of about 1.1 fb(-1) accumulated with the D0 detector at the Fermilab Tevatron collider. This is the first direct measurement of the CP-violating mixing p…

Bs0lifetime measurement in theCP-odd decay channelBs0→J/ψ f0(980)

The lifetime of the $B^{0}_{s}$ meson is measured in the decay channel $B^{0}_{s} \to J/\psi\mbox{ }\pi^+ \pi^-$ with $880 \leq M_{\pi^+\pi^-} \leq 1080$ MeV/$c^2$, which is mainly a CP-odd state and dominated by the $f_{0}(980)$ resonance. In 10.4 fb$^{-1}$ of data collected with the D0 detector in Run II of the Tevatron, the lifetime of the $B^{0}_{s}$ meson is measured to be $\tau(B^{0}_{s}) = 1.70\pm 0.14 \mbox{ (stat)} \pm 0.05 \mbox{ (syst) ps}$. Neglecting CP violation in $B_s^0/\bar{B}_s^0$ mixing, the measurement can be translated into the width of the heavy mass eigenstate of the $B^0_s$, $\Gamma_H = 0.59 \pm 0.05 \mbox{ (stat)} \pm 0.02 \mbox{ (syst)} \mbox{ ps$^{-1}$}$.

A study of intermittency in Hadronic Z$^0$ Decays

The correlations in rapidity in hadron production from e+e- annihilation near the Z0 resonance were studied by means of the method of factorial moments, using data taken with the DELPHI detector at LEP. The parton shower hadronization model was found to be in quantitative agreement with the data, in contrast with previous results at lower energies. © 1990.

Search for flavor-changing-neutral-current D meson decays

We study the flavor-changing-neutral-current process c to u mu+ mu- using 1.3 fb^-1 of p p bar collisions at sqrt(s) = 1.96 TeV recorded by the D0 detector operating at the Fermilab Tevatron Collider. We see clear indications of the Ds+ and D+ to phi pi+ to mu+ mu- pi+ final states with significance greater than four standard deviations above background for the D+ state. We search for the continuum decay of D+ to pi+mu+mu- in the dimuon invariant mass spectrum away from the phi resonance. We see no evidence of signal above background and set a limit of B(D+ to pi+mu+mu-) &lt; 3.9 x 10^-6 at the 90% C.L. This limit places the most stringent constraint on new phenomena in the c to u mu+ mu- t…

Search for the standard model Higgs boson inℓν+jetsfinal states in9.7  fb−1ofpp¯collisions with the D0 detector

Searches for the Higgs boson have started as soon as the underlying model for particle mass generation has been proposed, and the search went on for several decades at LEP, Tevatron and LHC. Last year the ATLAS and CMS Collaborations at the Large Hadron Collider (LHC) have reported the observation of a new boson [1, 2]. At the same time the CDF and D0 Collaborations reported combined evidence for a particle, with a mass consistent with that of the new boson observed at LHC [3]. This thesis presents the search by the D0 collaboration for the SM Higgs boson using events containing one isolated charged lepton (l = e or μ), a significant imbalance in transverse energy (6ET ), and two or more je…

Multiplicity fluctuations in hadronic final states from the decay of the Z0

An analysis of the fluctuations in the phase space distribution of hadrons produced in the decay of 78829 Z0 has been carried out, using the method of factorial moments. The high statistics collected by the DELPHI experiment at LEP during 1990 allowed studies of the event sample both globally and in intervals of p(t) and multiplicity, and for different jet topologies and for single jets. A large contribution to the factorial moments of the one-dimensional data on rapidity with respect to the event axis comes from hard gluons. Details of factorial moments in two and three dimensions are presented. Influences of resonance decays have been studied by Monte Carlo simulation: one-dimensional fac…

Measurement of the spin density matrix for the rho(0), K*(0)(892) and phi produced in Z(0) decays

The spin density matrix elements for the rho(0), K-*0(892) and phi produced in hadronic Z(0) decays are measured in the DELPHI detector. There is no evidence for spin alignment of the K-*0(892) and phi, in the region x(p) less than or equal to 0.3 (x(p) = p/p(beam)), where rho(00) = 0.33 +/- 0.05 and rho(00) = 0.30 +/- 0.04, respectively. In the fragmentation region, x(p) greater than or equal to 0.4, there is some indication for spin alignment of the rho(0) and K-*0(892), since rho(00) = 0.43 +/- 0.05 and rho(00) = 0.46 +/- 0.08, respectively. These values are compared with those found in meson-induced hadronic reactions. For the phi, rho(00) = 0.30 +/- 0.04 for x(p) greater than or equal …

Improved W boson mass measurement with the DO detector

We have measured the W boson mass using the DO detector and a data sample of 82 pb(-1) from the Fermilab Tevatron collider. This measurement uses W-->enu decays, where the electron is close to a boundary of a central electromagnetic calorimeter module. Such "edge" electrons have not been used in any previous DO analysis, and represent a 14% increase in the W boson sample size. For these electrons, new response and resolution parameters are determined, and revised backgrounds and underlying event energy flow measurements are made. When the current measurement is combined with previous DO W boson mass measurements, we obtain M-W=80.483+/-0.084 GeV. The 8% improvement from the previous DO meas…

Classification of the hadronic decays of the Z$^0$ into b and c quark pairs using a neural network

A classifier based on a feed-forward neural network has been used for separating a sample of about 123 500 selected hadronic decays of the Z 0 , collected by DELPHI during 1991, into three classes according to the flavour of the original quark pair: u u +d d +s s (unresolved), c c and b b . The classification has been used to compute the partial widths of the Z 0 into b and c quark pairs. This gave Γ c c /Γ h = 0.151 ± 0.008 ( stat. ) ± 0.041 ( syst. ) , Γ b b /Γ h = 0.232±0.005 ( stat. )±0.017 ( syst. ) .

Measurement of the normalized Z/γ∗→μ+μ− transverse momentum distribution in pp¯ collisions at s=1.96 TeV

We present a new measurement of the Z/gamma* transverse momentum distribution in the range 0-330 GeV, in proton-antiproton collisions at root s = 1.96 TeV. The measurement uses 0.97 fb(-1) of integrated luminosity recorded by the D0 experiment and is the first using the Z/gamma* -> mu(+)mu(-) + X channel at this center-of-mass energy. This is also the first measurement of the Z/gamma* transverse momentum distribution that presents the result at the level of particles entering the detector, minimizing dependence on theoretical models. As any momentum of the Z/gamma* in the plane transverse to the incoming beams must be balanced by some recoiling system, primarily the result of QCD radiation …

Search for charged Higgs bosons in decays of top quarks

We present a search for charged Higgs bosons in decays of top quarks, in the mass range $80 &lt; m_{H^{\pm} &lt; 155$ GeV, assuming the subsequent decay $H^{+} \to ��^{+} ��_��$ (and its charge conjugate). Using 0.9 fb$^{-1}$ of lepton+jets data collected with the D0 detector at the Fermilab Tevatron $p\bar{p}$ collider, operating at a center of mass energy $\sqrt{s}=1.96$ TeV, we find no evidence for a $H^{\pm}$ signal. Hence, we exclude branching ratios $B(t \to H^+b) &gt; 0.24$ for $m_{H^{\pm}=80$ GeV, and $B(t \to H^+b) &gt; 0.19$ for $m_{H^{\pm}=155$ GeV, at the 95% C.L.

Precise measurement of the top quark mass in the dilepton channel at D0

We measure the top quark mass (mt) in ppbar collisions at a center of mass energy of 1.96 TeV using dilepton ttbar-&gt;W+bW-bbar-&gt;l+nubl-nubarbbar events, where l denotes an electron, a muon, or a tau that decays leptonically. The data correspond to an integrated luminosity of 5.4 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider. We obtain mt = 174.0 +- 1.8(stat) +- 2.4(syst) GeV, which is in agreement with the current world average mt = 173.3 +- 1.1 GeV. This is currently the most precise measurement of mt in the dilepton channel.

Measurement of $\Delta^{++}$(1232) production in hadronic Z decays

A measurement of the \Delta^{++}(1232) inclusive production in hadronic decays of the Z at LEP is presented, based on 1.3 million hadronic events collected~ by the DELPHI~ detector in the 1994 LEP running~ period. The DELPHI ring imaging Cherenkov counters are used for identifying hadrons. The average \Delta^{++}(1232) multiplicity per hadronic event is 0.079 \pm 0.015 which is more than a factor of two below the JETSET, HERWIG and UCLA model predictions. It agrees with a recently proposed universal mass dependence of particle production rates in e^{+}e^- annihilations.

Model independent search for new phenomena inpp¯collisions ats=1.96  TeV

We describe a model independent search for physics beyond the standard model in lepton final states. We examine 117 final states using 1.1 fb$^{-1}$ of $p \bar{p}$ collisions data at $\sqrt{s} = 1.96$ TeV collected with the D0 detector. We conclude that all observed discrepancies between data and model can be attributed to uncertainties in the standard model background modeling, and hence we do not see any evidence for physics beyond the standard model.

Measurements of differential cross sections of Z/γ∗+jets+X events in pp¯ collisions at s=1.96 TeV

We present cross section measurements for Z/gamma* + jets + X production, differential in the transverse momenta of the three leading jets. The data sample was collected with the DO detector at the Fermilab Tevatron p (p) over bar collider at a center-of-mass energy of 1.96 TeV and corresponds to an integrated luminosity of 1 fb(-1). Leading and next-to-leading order perturbative QCD predictions are compared with the measurements. and agreement is found within the theoretical and experimental uncertainties. We also make comparisons with the predictions of four event generators. Two parton-shower-based generators show significant shape and normalization differences with respect to the data. …

Odderon Exchange from Elastic Scattering Differences between pp and pp¯ Data at 1.96 TeV and from pp Forward Scattering Measurements

We describe an analysis comparing the p p ¯ elastic cross section as measured by the D0 Collaboration at a center-of-mass energy of 1.96 TeV to that in p p collisions as measured by the TOTEM Collaboration at 2.76, 7, 8, and 13 TeV using a model-independent approach. The TOTEM cross sections, extrapolated to a center-of-mass energy of s = 1.96 TeV , are compared with the D0 measurement in the region of the diffractive minimum and the second maximum of the p p cross section. The two data sets disagree at the 3.4 σ level and thus provide evidence for the t -channel exchange of a colorless, C -odd gluonic compound, also known as the odderon. We combine these results with a TOTEM analysis of th…

Measurement of correlations between pions from different W's in e+e- → W+W- events

Correlations between pions from different W's in e(+)e(-) --> W+W- events are studied using data collected by the DELPHI detector at LEP running at a centre-of-mass energy of 172 GeV in 1996. At the present level of statistics, no enhancement of the correlation function above that expected from a pair of uncorrelated W's is observed at small values of the four-momentum difference of the pions. (C) 1997 Published by Elsevier Science B.V.

Search for violation of Lorentz invariance in top quark pair production and decay

Using data collected with the D0 detector at the Fermilab Tevatron Collider, corresponding to 5.3 fb$^{-1}$ of integrated luminosity, we search for violation of Lorentz invariance by examining the \ttbar production cross section in lepton+jets final states. We quantify this violation using the standard-model extension framework, which predicts a dependence of the \ttbar production cross section on sidereal time as the orientation of the detector changes with the rotation of the Earth. Within this framework, we measure components of the matrices $(c_Q)_{\mu\nu 33}$ and $(c_U)_{\mu\nu 33}$ containing coefficients used to parametrize violation of Lorentz invariance in the top quark sector. Wit…

Measurement of the tt¯ production cross section in pp¯ collisions at s=1.96 TeV in dilepton final states

We present a measurement of the top quark pair ($t\bar{t}$) production cross section ($\sigma_{t\bar{t}}$) in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using 230 pb$^{-1}$ of data collected by the D0 experiment at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), missing transverse energy, and jets in the final state. We employ lifetime-based b-jet identification techniques to further enhance the $t\bar{t}$ purity of the selected sample. For a top quark mass of 175 GeV, we measure $\sigma_{t\bar{t}}=8.6^{+1.6}_{-1.5}(stat.+syst.)\pm 0.6(lumi.)$ pb, in agreement with the standard model expectation

Precise measurement of the top quark mass in dilepton decays using optimized neutrino weighting

We measure the top quark mass in dilepton final states of top-antitop events in proton-antiproton collisions at sqrt(s) = 1.96 TeV, using data corresponding to an integrated luminosity of 9.7 fb^-1 at the Fermilab Tevatron Collider. The analysis features a comprehensive optimization of the neutrino weighting method to minimize the statistical uncertainties. We also improve the calibration of jet energies using the calibration determined in top-antitop to lepton+jets events, which reduces the otherwise limiting systematic uncertainty from the jet energy scale. The measured top quark mass is mt = 173.32 +/- 1.36(stat) +/- 0.85(syst) GeV.

Two-particle angular correlations in e(+)e(-) interactions compared with QCD predictions

Two-particle angular correlations in jet cones have been measured in e(+)e(-) annihilation into hadrons at LEP energies (root s = 91 and 183 GeV) and are compared with QCD predictions using the LPHD hypothesis. Two different functions have been tested. While the differentially normalized correlation function shows substantial deviations from the predictions, a globally normalized correlation function agrees well. The size of alpha(s)(eff) land other QCD parameters) and its running with the relevant angular scale, the validity of LPHD, and problems due to non-perturbative effects are discussed critically. (C) 1998 Elsevier Science B.V. All rights reserved.

Measurement of the shape of the boson rapidity distribution forpp¯→Z/γ*→e+e−+Xevents produced atsof 1.96 TeV

We present a measurement of the shape of the boson rapidity distribution for p (p) over bar -> Z/gamma(*)-> e(+)e(-)+X events at a center-of-mass energy of 1.96 TeV. The measurement is made for events with electron-positron mass 71 < M-ee < 111 GeV and uses 0.4 fb(-1) of data collected at the Fermilab Tevatron collider with the D0 detector. This measurement significantly reduces the uncertainties on the rapidity distribution in the forward region compared with previous measurements. Predictions of next-to-next-to-leading order (NNLO) QCD are found to agree well with the data over the full rapidity range.

Search for scalar leptoquarks and T-odd quarks in the acoplanar jet topology using of collision data at

A search for new physics in the acoplanar jet topology has been performed in 2.5 fb(-1) of data from p (p) over bar collisions at root s = 1.96 TeV, recorded by the DO detector at the Fermilab Tevatron Collider. The numbers of events with exactly two acoplanar jets and missing transverse energy are in good agreement with the Standard Model expectations. The result of this search has been used to set a lower mass limit of 205 GeV at the 95% C.L. on the mass of a scalar leptoquark when this particle decays exclusively into a quark and a neutrino. In the framework of the Little Higgs model with T-parity, limits have also been obtained on the T-odd quark mass as a function of the T-odd photon m…

A precise measurement of the Z resonance parameters through its hadronic decays

A measurement of the cross section for e+e-→ hadrons using 11 000 hadronic decays of the Z boson at ten different center-of-mass energies is presented. A three-parameter fit gives the following values for the Z mass MZ, the total width ΓZ, the product of the electronic and hadronic partial widths ΓeΓh, and the unfolded pole cross section σ0: MZ = 91.171 ± 0.030 (stat.) ± 0.030 (beam) GeV, ΓZ = 2.511 ± 0.065 GeV, ΓeΓh = 0.148 ± 0.006 (stat.) ± 0.004 (syst.) GeV2, σ0 = 41.6 ± 0.7 (stat.) ± 1.1 (syst.) nb, Good agreement with the predictions of the standard model is observed. From a two-parameter fit the number of massless neutrino generations is found to be Nv = 2.91 ± 0.26. Thus the hypothes…

Measurement of the differential cross sections for isolated direct photon pair production in pp¯ collisions at s=1.96 TeV

We present measurements of direct photon pair production cross sections using 8.5 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron p (p) over bar collider. The results are presented as differential distributions of the photon pair invariant mass d sigma/dM(gamma gamma), pair transverse momentum d sigma/dp(T)(gamma gamma) azimuthal angle between the photons d sigma/d Delta(phi)(gamma gamma), and polar scattering angle in the Collins-Soper frame d sigma/d vertical bar cos theta*vertical bar. Measurements are performed for isolated photons with transverse momenta p(T)(gamma) > 18 (17) GeV for the leading (next-to-leading) photon in P-T, pseudorapidities vertical bar eta(g…

Search for Higgs Boson Production in Dilepton and Missing Energy Final States with5.4  fb−1ofpp¯Collisions ats=1.96  TeV

A search for the standard model Higgs boson is presented using events with two charged leptons and large missing transverse energy selected from 5.4 fb-1 of integrated luminosity in p-pbar collisions at sqrt(s)=1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. No significant excess of events above background predictions is found, and observed (expected) upper limits at 95% confidence level on the rate of Higgs boson production are derived that are a factor of 1.55 (1.36) above the predicted standard model cross section at Higgs boson mass of 165 GeV.

Subjet multiplicity of gluon and quark jets reconstructed with thek⊥algorithm inpp¯collisions

The D empty set Collaboration has studied for the first time the properties of hadron-collider jets reconstructed with a successive-combination algorithm based on relative transverse momenta (k(perpendicular to)) of energy clusters. Using the standard value D = 1.0 of the jet-separation parameter in the k(perpendicular to) algorithm, we find that the p(T) of such jets is higher than the E-T of matched jets reconstructed with cones of radius R = 0.7, by about 5 (8) GeV at p(T) approximate to90 (240) GeV. To examine internal jet structure, the k(perpendicular to) algorithm is applied within D = 0.5 jets to resolve any subjets. The multiplicity of subjets in jet samples at roots = 1800 GeV and…

Measurement of the lifetime difference in the B$_s^0$ system

We present a study of the decay B_s^0 -> J/psi phi We obtain the CP-odd fraction in the final state at time zero, R_perp = 0.16 +/- 0.10 (stat) +/- 0.02 (syst), the average lifetime of the (B_s, B_sbar) system, tau (B_s^0) =1.39^{+0.13}_{-0.16} (stat) ^{+0.01}_{-0.02} (syst) ps, and the relative width difference between the heavy and light mass eigenstates, Delta Gamma/Gamma = (Gamma_L - Gamma_H)/Gamma =0.24^{+0.28}_{-0.38} (stat) ^{+0.03}_{-0.04} (syst). With the additional constraint from the world average of the B_s^0$lifetime measurements using semileptonic decays, we find tau (B_s^0)= 1.39 +/- 0.06 ~ps and Delta Gamma/\Gamma = 0.25^{+0.14}_{-0.15}. For the ratio of the B_s^0 and B^0 li…

Measurement of the Forward-Backward Charge Asymmetry and Extraction ofsin2θWeffinpp¯→Z/γ*+X→e+e−+XEvents Produced ats=1.96  TeV

We present a measurement of the forward-backward charge asymmetry ($A_{FB}$) in $p\bar{p} \to Z/\gamma^{*}+X \to e^+e^-+X$ events at a center-of-mass energy of 1.96 TeV using 1.1 fb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron collider. $A_{FB}$ is measured as a function of the invariant mass of the electron-positron pair, and found to be consistent with the standard model prediction. We use the $A_{FB}$ measurement to extract the effective weak mixing angle $sin^2Theta^{eff}_W = 0.2327 \pm 0.0018 (stat.) \pm 0.0006 (syst.)$.

First Study of the Radiation-Amplitude Zero inWγProduction and Limits on AnomalousWWγCouplings ats=1.96  TeV

We present results from a study of p (p) over bar -> W gamma+X events utilizing data corresponding to 0.7 fb(-1) of integrated luminosity at root s = 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We set limits on anomalous WW gamma couplings at the 95% C.L. The one-dimensional 95% C.L. limits are 0.49 <kappa(gamma)< 1.51 and -0.12 <lambda(gamma)< 0.13. We make the first study of the charge-signed rapidity difference between the lepton and the photon and find it to be indicative of the standard model radiation-amplitude zero in the W gamma system.

Energy dependence of the differences between the quark and gluon jet fragmentation

Three jet events arising from decays of the Z beson, collected by the DELPHI detector, were used to measure differences in quark and gluon fragmentation. Gluon jets were anti-tagged by identifying b quark jets. Unbiased quark jets came from events with two jets plus one photon. Quark and gluon jet properties in different energy ranges were compared for the first time within the same detector. Quark and gluon jets of nearly the same energy in symmetric three jet event topologies were also compared. Using three independent methods, the average value of the ratio of the mean charged multiplicities of gluon and quark jets is [ r ] = 1.241 +/- 0.015 (stat.) +/- 0.025 (syst.). Gluon jets are broa…

Search for Violation ofCPTand Lorentz Invariance inBs0Meson Oscillations

We present the first search for CPT-violating effects in the mixing of B-s(0) mesons using the full Run II data set with an integrated luminosity of 10.4 fb(-1) of proton-antiproton collisions coll ...

Model-independent measurement of t-channel single top quark production in pp¯ collisions at s=1.96 TeV

We present a model-independent measurement of $t$-channel electroweak production of single top quarks in $\ppbar$ collisions at $\sqrt{s}=1.96\;\rm TeV$. Using $5.4\;\rm fb^{-1}$ of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider, and selecting events containing an isolated electron or muon, missing transverse energy and one or two jets originating from the fragmentation of $b$ quarks, we measure a cross section $\sigma({\ppbar}{\rargap}tqb+X) = 2.90 \pm 0.59\;\rm (stat+syst)\; pb$ for a top quark mass of $172.5\;\rm GeV$. The probability of the background to fluctuate and produce a signal as large as the one observed is $1.6\times10^{-8}$, corresponding…

Search for charged massive long-lived particles

We report on a search for charged massive long-lived particles (CMLLPs), based on 5.2 fb$^{-1}$ of integrated luminosity collected with the D0 detector at the Fermilab Tevatron $p\bar{p}$ collider. We search for events in which one or more particles are reconstructed as muons but have speed and ionization energy loss $(dE/dx)$ inconsistent with muons produced in beam collisions. CMLLPs are predicted in several theories of physics beyond the standard model. We exclude pair-produced long-lived gaugino-like charginos below 267 GeV and higgsino-like charginos below 217 GeV at 95% C.L., as well as long-lived scalar top quarks with mass below 285 GeV.

Study of DirectCPViolation inB±→J/ψK±(π±)Decays

We present a search for direct CP violation in $B^{\pm} \to J/\psi K^{\pm}(\pi^{\pm})$ decays. The event sample is selected from 2.8 fb$^{-1}$ of $p\bar{p}$ collisions recorded by D0 experiment in Run II of the Fermilab Tevatron Collider. The charge asymmetry $A_{CP}(B^+ \to J/\psi K^+) = +0.0075 \pm 0.0061$(stat.)$\pm 0.0027$(syst.) is obtained using a sample of approximately 40 thousand $B^{\pm} \to J/\psi K^{\pm}$ decays. The achieved precision is of the same level as the expected deviation predicted by some extensions of the standard model. We also measured the charge asymmetry $A_{CP}(B^+ \to J/\psi \pi^+) = -0.09 \pm 0.08$(stat.)$\pm 0.03$(syst.).

Tevatron Run II combination of the effective leptonic electroweak mixing angle

The Ministry of Science and Innovation and the Consolider-Ingenio 2010 Program and the European Union community Marie Curie Fellowship Contract No. 302103.

Determination of the pole and MS¯ masses of the top quark from the tt¯ cross section

We use higher-order quantum chromodynamics calculations to extract the mass of the top quark from the ttbar cross section measured in the lepton+jets channel in ppbar collisions at sqrt(s)=1.96 TeV using 5.3 fb-1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider. The extracted top quark pole mass and MSbar mass are compared to the current Tevatron average top quark mass obtained from direct measurements.

Search for a narrowtt¯resonance inpp¯collisions ats=1.96  TeV

We report a search for a narrow ttbar resonance that decays into a lepton+jets final state based on an integrated luminosity of 5.3/fb of proton-antiproton collisions at sqrt{s}=1.96 TeV collected by the D0 Collaboration at the Fermilab Tevatron Collider. We set upper limits on the production cross section of such a resonance multiplied by its branching fraction to ttbar which we compare to predictions for a leptophobic topcolor Z' boson. We exclude such a resonance at the 95% confidence level for masses below 835 GeV.

Experimental study of the triple-gluon vertex

Abstract In four-jet events from e+e− →Z0 →multihadrons one can separate the three principal contributions from the triple-gluon vertex, double gluon-bremsstrahlung and the secondary quark-antiquark production, using the shape of the two-dimensional angular distributions in the generalized Nachtmann-Reiter angle θ NR ∗ and the opening angle of the secondary jets. Thus one can identify directly the contribution from the triple-gluon vertex without comparison with a specific non-QCD model. Applying this new method to events taken with the DELPHI-detector we get for the ratio of the colour factor Nc to the fermionic Casimir operator C F : N c C F = 2.55 ± 0.55 ( stat. ) ± 0.4 ( fragm. + models…

Measurement of the muon charge asymmetry from W boson decays

We present a measurement of the muon charge asymmetry from W boson decays using 0.3 fb^{-1} of data collected at \sqrt{s}=1.96 GeV between 2002 and 2004 with the D0 detector at the Fermilab Tevatron ppbar Collider. We compare our findings with expectations from next-to-leading-order calculations performed using the CTEQ6.1M and MRST04 NLO parton distribution functions. Our findings can be used to constrain future parton distribution function fits.

Combined search for the Higgs boson with the D0 experiment

We perform a combination of searches for standard model Higgs boson production in $p\bar{p}$ collisions recorded by the D0 detector at the Fermilab Tevatron Collider at a center of mass energy of $\sqrt{s}=1.96$ TeV. The different production and decay channels have been analyzed separately, with integrated luminosities of up to 9.7 fb$^{-1}$ and for Higgs boson masses $90\leq M_H \leq 200$ GeV. We combine these final states to achieve optimal sensitivity to the production of the Higgs boson. We also interpret the combination in terms of models with a fourth generation of fermions, and models with suppressed Higgs boson couplings to fermions. The result excludes a standard model Higgs boson …

Search for anomalous top-quark couplings with the D0 detector

Anomalous Wtb couplings modify the angular correlations of the top quark decay products and change the single top quark production cross section. We present limits on anomalous top quark couplings by combining information from W boson helicity measurements in top quark decays and anomalous coupling searches in the single top quark final state. We set limits on right-handed vector couplings as well as left-handed and right-handed tensor couplings based on about 1fb^-1 of data collected by the D0 experiment.

Measurement ofγ+b+Xandγ+c+XProduction Cross Sections inpp¯Collisions ats=1.96  TeV

First measurements of the differential cross sections for the inclusive production of a photon in association with a heavy quark (c, b) jet are presented, covering photon transverse momenta 30-150 GeV, photon rapidities | y_gamma| 15 GeV. The results are based on an integrated luminosity of 1 fb^-1 in ppbar collisions at sqrt(s)=1.96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider. The results are compared with next-to-leading order perturbative QCD predictions.

Search for a heavy resonance decaying into aZ+jetfinal state inpp¯collisions ats=1.96  TeVusing the D0 detector

We have searched for a heavy resonance decaying into a Z+jet final state in p (p) over bar collisions at a center of mass energy of 1.96 TeV at the Fermilab Tevatron collider using the D0 detector. No indication for such a resonance was found in a data sample corresponding to an integrated luminosity of 370 pb(-1). We set upper limits on the cross section times branching fraction for heavy resonance production at the 95% C.L. as a function of the resonance mass and width. The limits are interpreted within the framework of a specific model of excited quark production.

Measurement of $B_d$ mixing using opposite-side flavor tagging

We report on a measurement of the $B^0_d$ mixing frequency and the calibration of an opposite-side flavor tagger in the D{\O}experiment. Various properties associated with the $b$ quark on the opposite side of the reconstructed $B$ meson were combined using a likelihood-ratio method into a single variable with enhanced tagging power. Its performance was tested with data, using a large sample of reconstructed semileptonic $B \to \mu \dzero X$ and $B \to \mu \dst X$ decays, corresponding to an integrated luminosity of approximately 1 fb$^{-1}$. The events were divided into groups depending on the value of the combined tagging variable, and an independent analysis was performed in each group. …

Search for resonant second generation slepton production at the Fermilab Tevatron

Made available in DSpace on 2022-04-28T20:09:02Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-01-01 We present a search for supersymmetry in the R-parity violating resonant production and decay of smuons and muon sneutrinos in the channels, 2,3,40. We analyzed 0.38fb-1 of integrated luminosity collected between April 2002 and August 2004 with the D0 detector at the Fermilab Tevatron Collider. The observed number of events is in agreement with the standard model expectation, and we calculate 95% C.L. limits on the slepton production cross section times branching fraction to gaugino plus muon, as a function of slepton and gaugino masses. In the framework of minimal supergravity, we s…

Measurement of Inclusive Differential Cross Sections forΥ(1S)Production inpp¯Collisions ats=1.96   TeV

We present measurements of the inclusive production cross sections of the Upsilon(1S) bottomonium state in p (p) over bar collisions at root s=1.96 TeV. Using the Upsilon(1S)->mu(+)mu(-) decay mode for a data sample of 159 +/- 10 pb(-1) collected by the D0 detector at the Fermilab Tevatron collider, we determine the differential cross sections as a function of the Upsilon(1S) transverse momentum for three ranges of the Upsilon(1S) rapidity: 0 <\y(Upsilon)\<= 0.6, 0.6 <\y(Upsilon)\<= 1.2, and 1.2 <\y(Upsilon)\<= 1.8.

Observation of a narrow mass state decaying intoΥ(1S)+γinpp¯collisions ats=1.96  TeV

Using data corresponding to an integrated luminosity of 1.3 fb(-1), we observe a narrow mass state decaying into Gamma(1S) + gamma, where the Gamma(1S) meson is detected by its decay into a pair of oppositely charged muons, and the photon is identified through its conversion into an electron-positron pair. The significance of this observation is 5.6 standard deviations. The mass of the state is centered at 10.551 +/- 0.014(stat) +/- 0.017(syst) GeV/c(2), which is consistent with that of the state recently observed by the ATLAS Collaboration.

Measurement of spin correlation between top and antitop quarks produced in pp¯ collisions at s=1.96 TeV

Department of Energy (United States of America); National Science Foundation (United States of America); Alternative Energies and Atomic Energy Commission (France); National Center for Scientific Research/ National Institute of Nuclear and Particle Physics (France); Ministry of Education and Science of the Russian Federation (Russia); National Research Center "Kurchatov Institute" of the Russian Federation (Russia); Russian Foundation for Basic Research (Russia); National Council for the Development of Science and Technology (Brazil); Carlos Chagas Filho Foundation for the Support of Research in the State of Rio de Janeiro (Brazil); Department of Atomic Energy (India); Department of Science…

Measurement of the production fraction times branching fractionf(b→Λb)·B(Λb→J/ψΛ)

The \Lambda_b(udb) baryon is observed in the decay \Lambda_b --> J/\psi \Lambda using 6.1 fb^{-1} of p\bar{p} collisions collected with the D0 detector at \sqrt{s}=1.96 TeV. The production fraction multiplied by the branching fraction for this decay relative to that for the decay B^0 --> J/\psi K^0_s is measured to be 0.345 \pm 0.034 (stat.) \pm 0.033 (syst.) \pm 0.003 (PDG). Using the world average value of f(b --> B^0)B(B^0 --> J/\psi K^0_s) = (1.74 \pm 0.08) \times 10^{-5}, we obtain f(b --> \Lambda_b)B(\Lambda_{b} --> J/\psi \Lambda) = (6.01 \pm 0.60 (stat.) \pm 0.58 (syst.) \pm 0.28 (PDG)) \times 10^{-5}. This measurement represents an improvement in precision by about a factor of thre…

Search for Resonant Pair Production of Neutral Long-Lived Particles Decaying tobb¯inpp¯Collisions ats=1.96  TeV

We report on a first search for resonant pair production of neutral long-lived particles (NLLP) which each decay to a b (b) over bar pair, using 3.6 fb(-1) of data recorded with the D0 detector at the Fermilab Tevatron collider. We search for pairs of displaced vertices in the tracking detector at radii in the range 1.6-20 cm from the beam axis. No significant excess is observed above background, and upper limits are set on the production rate in a hidden-valley benchmark model for a range of Higgs boson masses and NLLP masses and lifetimes.

Search for W ' bosons decaying to an electron and a neutrino with the D0 detector

This Letter describes the search for a new heavy charged gauge boson W' decaying into an electron and a neutrino. The data were collected with the D0 detector at the Fermilab Tevatron proton-antiproton Collider at a center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity of about 1 inverse femtobarn. Lacking any significant excess in the data in comparison with known processes, an upper limit is set on the production cross section times branching fraction, and a W' boson with mass below 1.00 TeV can be excluded at the 95% C.L., assuming standard-model-like couplings to fermions. This result significantly improves upon previous limits, and is the most stringent to date.

Precise Study of theZ/γ*Boson Transverse Momentum Distribution inpp¯Collisions Using a Novel Technique

Using 7.3 pb-1 of ppbar collisions collected by the D0 detector at the Fermilab Tevatron, we measure the distribution of the variable \phistar, which probes the same physical effects as the Z/gamma* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. A QCD prediction is found to describe the general features of the \phistar distribution, but is unable to describe its detailed shape or dependence on boson rapidity. A prediction that includes a broadening of transverse momentum for small values of the parton momentum fraction is strongly disfavored.

Evidence for s-channel single top quark production in pp¯ collisions at s=1.96 TeV

We present measurements of the cross sections for the two main production modes of single top quarks in p (p) over bar collisions at root s = 1.96 TeV in the Run II data collected with the DO detector at the Fermilab Tevatron Collider, corresponding to an integrated luminosity of 9.7 fb(-1). The s-channel cross section is measured to be sigma(p (p) over bar -> tb + X) = 1.10(-0.31)(+0.33) pb with no assumptions on the value of the t-channel cross section. Similarly, the t-channel cross section is measured to be sigma(p (p) over bar -> tqb + X) = 3.07(-0.49)(+0.54) pb. We also measure the s + t combined cross section as sigma(p (p) over bar -> tb + X, tqb + X) = 4.11(-0.55)(+0.60) ph and set…

Search for large extra dimensions via single photon plus missing energy final states at s=1.96TeV

Made available in DSpace on 2022-04-28T20:42:17Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-06-30 We report on a search for large extra dimensions in a data sample of approximately 1fb-1 of pp̄ collisions at s=1.96TeV. We investigate Kaluza-Klein graviton production with a photon and missing transverse energy in the final state. At the 95% C.L. we set limits on the fundamental mass scale MD from 884to 778GeV for two to eight extra dimensions. © 2008 The American Physical Society. Universidad de Buenos Aires, Buenos Aires LAFEX Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro Universidade Do Estado Do Rio de Janeiro, Rio de Janeiro Universidade Federal Do ABC, Santo André In…

Search for long-lived charged massive particles with the D0 detector

Made available in DSpace on 2022-04-28T20:51:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-04-22 Science and Technology Facilities Council We search for long-lived charged massive particles using 1.1fb-1 of data collected by the D0 detector at the Fermilab Tevatron pp̄ Collider. Time-of-flight information is used to search for pair produced long-lived tau sleptons, gauginolike charginos, and Higgsino-like charginos. We find no evidence of a signal and set 95% C.L. cross section upper limits for staus, which vary from 0.31 to 0.04 pb for stau masses between 60 and 300 GeV. We also set lower mass limits of 206 GeV (171 GeV) for pair produced charged gauginos (Higgsinos). © 2009 Th…

A Search for Heavy Stable and Long-Lived Squarks and Sleptons in $e^+ e^-$ Collisions at Energies from 130 to 183 GeV

A search for stable and long-lived heavy charged particles used the data taken by the DELPHI experiment at energies from 130 to 183 GeV. The Cherenkov light detected in the Ring Imaging Cherenkov Detector and the ionization loss measured in the Time Projection Chamber identify heavy particles from masses of 2 to nearly 89 GeV/c$^2$. Upper limits are given on the production cross-section and masses of sleptons, free squarks with a charge of $q = \pm 2/3e$ and hadronizing squarks. A search for stable and long-lived heavy charged particles used the data taken by the DELPHI experiment at energies from 130 to 183 GeV. The Cherenkov light detected in the Ring Imaging Cherenkov Detector and the io…

Measurement of the Polarization of theΥ(1S)andΥ(2S)States inpp¯Collisions ats=1.96  TeV

We present a study of the polarization of the $\Upsilon(1S)$ and $\Upsilon(2S)$ states using a $1.3 $ fb$^{-1}$ data sample collected by the D0 experiment in 2002--2006 during Run II of the Fermilab Tevatron Collider. We measure the polarization parameter $\alpha=(\sigma_{T}-2\sigma_{L})/(\sigma_{T}+2\sigma_{L})$, where $\sigma_{T}$ and $\sigma_{L}$ are the transversely and longitudinally polarized components of the production cross section, as a function of the transverse momentum ($p_{T}^{\Upsilon}$) for the $\Upsilon(1S)$ and $\Upsilon(2S)$. Significant $p_{T}^{\Upsilon}$-dependent longitudinal polarization is observed for the $\Upsilon(1S)$. A comparison with theoretical models is prese…

Search for Single Vectorlike Quarks inpp¯Collisions ats=1.96  TeV

We present a search for hypothetical vector-like quarks in ppbar collisions at sqrt(s) = 1.96 TeV. The data were collected by the D0 detector at the Fermilab Tevatron Collider and correspond to an integrated luminosity of 5.4 fb^(-1). We select events with a final state composed of a W or Z boson and a jet consistent with a heavy object decay. We observe no significant excess in comparison to the background prediction and set limits on production cross sections for vector-like quarks decaying to W+jet and Z+jet. These are the most stringent mass limits for electroweak single vector-like quark production at hadron colliders.

Search for Large Extra Spatial Dimensions in the Dielectron and Diphoton Channels inpp¯Collisions ats=1.96  TeV

We report on a search for large extra spatial dimensions in the dielectron and diphoton channels using a data sample of 1.05 \invfb of \ppb collisions at a center-of-mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. The invariant mass spectrum of the data agrees well with the prediction of the standard model. We find 95% C.L. lower limits on the effective Planck scale between 2.1 and 1.3 TeV for 2 to 7 extra dimensions.

A novel method for modeling the recoil in W boson events at hadron collider

We present a new method for modeling the hadronic recoil in W-&gt;lnu events produced at hadron colliders. The recoil is chosen from a library of recoils in Z-&gt;ll data events and overlaid on a simulated W-&gt;lnu event. Implementation of this method requires that the data recoil library describe the properties of the measured recoil as a function of the true, rather than the measured, transverse momentum of the boson. We address this issue using a multidimensional Bayesian unfolding technique. We estimate the statistical and systematic uncertainties from this method for the W boson mass and width measurements assuming 1 fb-1 of data from the Fermilab Tevatron. The uncertainties are found…

Measurement of direct photon pair production cross sections in pp¯ collisions at s=1.96 TeV

We present a measurement of direct photon pair production cross sections using 4.2 fb(-1) of data collected with the DO detector at the Fermilab Tevatron p (p) over bar Collider. We measure single differential cross sections as a function of the diphoton mass, the transverse momentum of the diphoton system, the azimuthal angle between the photons, and the polar scattering angle of the photons. In addition, we measure double differential cross sections considering the last three kinematic variables in three diphoton mass bins. The results are compared with different perturbative QCD predictions and event generators. (C) 2010 Elsevier B.V. All rights reserved.

Search for the Higgs boson in lepton, tau and jets final states

We present a search for the standard model Higgs boson in final states with an electron or muon and a hadronically decaying tau lepton in association with two or more jets using 9.7 fb^{-1} of Run II Fermilab Tevatron Collider data collected with the D0 detector. The analysis is sensitive to Higgs boson production via gluon fusion, associated vector boson production, and vector boson fusion, followed by the Higgs boson decay to tau lepton pairs or to W boson pairs. The ratios of 95% C.L. upper limits on the cross section times branching ratio to those predicted by the standard model are obtained for orthogonal subsamples that are enriched in either H -&gt; tau tau decays or H -&gt; WW decay…

Study of the four-jet anomaly observed at LEP centre-of-mass energies of 130 and 136 GeV

The four-jet events collected by DELPHI during the special LEP run at centre-of-mass energies of 130 and 136 GeV in 1997 with an integrated luminosity of 5.9 pb(-1) are analysed. Their rate and the distributions of their di-jet masses, their smallest jet charges, and their di-jet charge separations all agree well with Standard Model predictions. Thus the hypothesis of pair production of a new particle with a sum of di-jet masses around 105 GeV/c(2) is not supported. The combined result of the four LEP collaborations refuting this hypothesis at over 99% confidence level is also given. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

Measurement of theCP-violation parameter ofB0mixing and decay withpp¯→μμXdata

We measure the dimuon charge asymmetry A in p (p) over bar collisions at a center of mass energy root s=1960 GeV. The data was recorded with the D0 detector and corresponds to an integrated luminosity of approximately 1.0 fb(-1). Assuming that the asymmetry A is due to asymmetric B-0 (B) over bar (0) mixing and decay, we extract the CP-violation parameter of B-0 mixing and decay: ((epsilon B0))/(1+vertical bar epsilon B0 vertical bar 2)=(AB0)/(4)= -0.0023 +/- 0.0011(stat)+/- 0.0008(syst).A(B)(0) is the dimuon charge asymmetry from decays of B-0(B) over bar (0) pairs. The general case, with CP violation in both B-0 and B-s(0) systems, is also considered. Finally we obtain the forward-backwar…

Measurement of the tt¯ production cross section using dilepton events in pp¯ collisions

We present a measurement of the a production cross section sigma((u) over bar) in p (p) over bar collisions at root s = 1.96 TeV using 5.4 fb(-1) of integrated luminosity collected with the D0 detector. We consider final states with at least two jets and two leptons (ee, e mu, mu mu), and events with one jet for the e mu final state as well. The measured cross section is sigma((u) over bar) = 7.36(-0.79)(+0.90)(stat + syst) pb. This result combined with the cross section measurement in the lepton + jets final state yields sigma((u) over bar) = 7.56(-0.56)(+0.63)(stat + syst) pb, which agrees with the standard model expectation. The relative precision of 8% of this measurement is comparable …

Limits on the production of scalar leptoquarks from $Z^0$ decays at LEP

A search has been made for pairs and for single production of scalar leptoquarks of the first and second generations using a data sample of 392000 Z0 decays from the DELPHI detector at LEP 1. No signal was found and limits on the leptoquark mass, production cross section and branching ratio were set. A mass limit at 95% confidence level of 45.5 GeV/c2 was obtained for leptoquark pair production. The search for the production of a single leptoquark probed the mass region above this limit and its results exclude first and second generation leptoquarks D0 with masses below 65 GeV/c2 and 73 GeV/c2 respectively, at 95% confidence level, assuming that the D0lq Yukawa coupling alpha(lambda) is equ…

Measurement of the W boson helicity in top quark decay at D0

We present a measurement of the fraction f_+ of right-handed W bosons produced in top quark decays, based on a candidate sample of ttbar events in the l+jets and dilepton decay channels corresponding to an integrated luminosity of 370 pb^-1 collected by the DO detector at the Fermilab Tevatron ppbar Collider at sqrt{s}=1.96 TeV. We reconstruct the decay angle theta^* for each lepton. By comparing the \cos\theta^* distribution from the data with those for the expected background and signal for various values of f_+, we find $f_+=0.056 +- 0.080 (stat) +- 0.057 (syst)}. (f_+ < 0.23 at 95% C.L.), consistent with the standard model prediction of f_+=3.6 x10^-4.

Measurement ofBs0Mixing Parameters from the Flavor-Tagged DecayBs0→J/ψϕ

From an analysis of the flavor-tagged decay B-s(0)-> J/psi phi we obtain the width difference between the B-s(0) light and heavy mass eigenstates, Delta Gamma(s)=0.19 +/- 0.07(stat)(-0.01)(+0.02)(syst) ps(-1), and the CP-violating phase, phi(s)=-0.57(-0.30)(+0.24)(stat)(-0.02)(+0.08)(syst). The allowed 90% CL intervals of Delta Gamma(s) and phi(s) are 0.06 <Delta Gamma(s)< 0.30 ps(-1) and -1.20 <phi(s)< 0.06, respectively. The data sample corresponds to an integrated luminosity of 2.8 fb(-1) accumulated with the D0 detector at the Fermilab Tevatron collider.

Search for single top quark production in pp¯ collisions at s=1.96 TeV

We present a search for electroweak production of single top quarks in the s-channel and t-channel using neural networks for signal-background separation. We have analyzed 230 pb(-1) of data collected with the DO detector at the Fermilab Tevatron Collider at a center-of-mass energy of 1.96 TeV and find no evidence for a single top quark signal. The resulting 95% confidence level upper limits on the single top quark production cross sections are 6.4 pb in the s-channel and 5.0 ph in the t-channel. (c) 2005 Elsevier B.V. All rights reserved.

Measurement of the lifetime of the Bc +- meson in the semileptonic decay channel

Using approximately 1.3 fb-1 of data collected by the D0 detector between 2002 and 2006, we measure the lifetime of the B_c meson in the B_c -> J/psi mu nu X final state. A simultaneous unbinned likelihood fit to the J/\psi+mu invariant mass and lifetime distributions yields a signal of 881 +/- 80 (stat) candidates and a lifetime measurement of \tau(B_c) = 0.448 +0.038 -0.036 (stat) +/- 0.032 (syst) ps.

A Measurement of Sin2-theta-w From the Charge Asymmetry of Hadronic Events At the Z0 Peak

Abstract View references (24)The weak mixing angle has been measured from the charge asymmetry of hadronic events with two different approaches using the DELPHI detector at LEP. Both methods are based on a momentum-weighted charge sum to determine the jet charge in both event hemispheres. In a data sample of 247 300 multihadronic Z0 decays a charge asymmetry of 〈QF〉 - 〈QB〉 = -0.0076±0.0012(stat.)±0.0005(exp. syst.)±0.0014(frag.) and a raw forward-backward asymmetry of Araw FB = -0.0109±0.0020(stat.)±0.0010(exp. syst.)±0.0017(frag.) have been measured. This result corresponds to a value of sinθeff=0.2345±0.0030(exp.)±0.0027(frag.) ,sin2θMS=0.2341±0.0030(exp.)±0. 0027(frag.) and to sin2θW=1-m…

Search for higgs bosons decaying to tau pairs in pp̄ collisions with the D0 detector

Made available in DSpace on 2022-04-28T20:43:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-08-14 Science and Technology Facilities Council We present a search for the production of neutral Higgs bosons decaying into τ+τ- final states in pp̄ collisions at a center-of-mass energy of 1.96 TeV. The data, corresponding to an integrated luminosity of approximately 1fb-1, were collected by the D0 experiment at the Fermilab Tevatron Collider. Limits on the production cross section times branching ratio are set. The results are interpreted in the minimal supersymmetric standard model yielding limits that are the most stringent to date at hadron colliders. © 2008 The American Physical Soc…

Evidence ofWWandWZProduction withlepton+jetsFinal States inpp¯Collisions ats=1.96  TeV

We present first evidence for WW+WZ production in lepton + jets final states at a hadron collider. The data correspond to 1.07 fb-1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron in pp collisions at square root s=1.96 TeV. The observed cross section for WW+WZ production is 20.2+/-4.5 pb, consistent with the standard model and more precise than previous measurements in fully leptonic final states. The probability that background fluctuations alone produce this excess is <5.4 x 10-6, which corresponds to a significance of 4.4 standard deviations.

Search for AssociatedWand Higgs Boson Production inpp¯Collisions ats=1.96   TeV

We present results of a search for WH -> l nu b (b) over bar production in p (p) over bar collisions based on the analysis of 1.05 fb(-1) of data collected by the D0 experiment at the Fermilab Tevatron, using a neural network for separating the signal from backgrounds. No signal-like excess is observed, and we set 95% C. L. upper limits on the WH production cross section multiplied by the branching ratio for H -> b (b) over bar for Higgs boson masses between 100 and 150 GeV. For a mass of 115 GeV, we obtain an observed (expected) limit of 1.5 (1.4) pb, a factor of 11.4 (10.7) times larger than the standard model prediction.

Determination of the width of the top quark

We extract the total width of the top quark, Gamma_t, from the partial decay width Gamma(t -&gt; W b) measured using the t-channel cross section for single top quark production and from the branching fraction B(t -&gt; W b) measured in ttbar events using up to 2.3 fb^-1 of integrated luminosity collected by the D0 Collaboration at the Tevatron ppbar Collider. The result is Gamma_t = 1.99 +0.69 -0.55 GeV, which translates to a top-quark lifetime of tau_t = (3.3 +1.3 -0.9) x 10^-25 s. Assuming a high mass fourth generation b' quark and unitarity of the four-generation quark-mixing matrix, we set the first upper limit on |Vtb'| &lt; 0.63 at 95% C.L.

Search for WH associated production in 5.3 fb−1 of pp¯ collisions at the Fermilab Tevatron

We present a search for associated production of Higgs and W bosons in collisions at a center of mass energy of in 5.3 fb−1 of integrated luminosity recorded by the D0 experiment. Multivariate an ...

Search for charged Higgs bosons in top quark decays

We present a search for charged Higgs bosons in top quark decays. We analyze the \eplus, \muplus, $ee$, $e\mu$, $\mu\mu$, \etau and \mutau final states from top quark pair production events, using data from about 1${\text{fb}}^{-1}$ of integrated luminosity recorded by the \dzero experiment at the Fermilab Tevatron Collider. We consider different scenarios of possible charged Higgs boson decays, one where the charged Higgs boson decays purely hadronically into a charm and a strange quark, another where it decays into a $\tau$ lepton and a $\tau$ neutrino and a third one where both decays appear. We extract limits on the branching ratio $B(t\to H^+ b)$ for all these models. We use two method…

Direct measurement of the mass difference between top and antitop quarks

We present a direct measurement of the mass difference between top and antitop quarks (dm) in lepton+jets top-antitop final states using the "matrix element" method. The purity of the lepton+jets sample is enhanced for top-antitop events by identifying at least one of the jet as originating from a b quark. The analyzed data correspond to 3.6 fb-1 of proton-antiproton collisions at 1.96 TeV acquired by D0 in Run II of the Fermilab Tevatron Collider. The combination of the e+jets and mu+jets channels yields dm = 0.8 +/- 1.8 (stat) +/- 0.5 (syst) GeV, which is in agreement with the standard model expectation of no mass difference.

Study of the X±(5568) state with semileptonic decays of the Bs0 meson

We present a study of the X±(5568) using semileptonic decays of the Bs0 meson using the full run II integrated luminosity of 10.4  fb-1 in proton-antiproton collisions at a center of mass energy of 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. We report evidence for a narrow structure, X±(5568), in the decay sequence X±(5568)→Bs0π± where Bs0→μ∓Ds±X, Ds±→ϕπ± which is consistent with the previous measurement by the D0 Collaboration in the hadronic decay mode, X±(5568)→Bs0π± where Bs0→J/ψϕ. The mass and width of this state are measured using a combined fit of the hadronic and semileptonic data, yielding m=5566.9-3.1+3.2(stat)-1.2+0.6(syst)  MeV/c2, Γ=18.6-6.1+7.9(s…

Search for anomalous quarticWWγγcouplings in dielectron and missing energy final states inpp¯collisions ats=1.96  TeV

We present a search for anomalous components of the quartic gauge boson coupling WW gamma gamma in events with an electron, a positron and missing transverse energy. The analyzed data correspond to 9.7 fb(-1) of integrated luminosity collected by the D0 detector in p (p) over bar collisions at root s 1.96 TeV. The presence of anomalous quartic gauge couplings would manifest itself as an excess of boosted WW events. No such excess is found in the data, and we set the most stringent limits to date on the anomalous coupling parameters a(0)(W) and a(C)(W). When a form factor with Lambda(cutoff) = 0.5 TeV is used, the observed upper limits at 95% C. L. are vertical bar a(0)(W)/Lambda(2)vertical …

Model-independent measurement of the W-boson helicity in top-quark decays at D0.

Made available in DSpace on 2022-04-28T20:37:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-02-14 Science and Technology Facilities Council We present the first model-independent measurement of the helicity of W bosons produced in top quark decays, based on a 1fb-1 sample of candidate tt̄ events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron pp̄ Collider. We reconstruct the angle θ* between the momenta of the down-type fermion and the top quark in the W boson rest frame for each top quark decay. A fit of the resulting cos θ* distribution finds that the fraction of longitudinal W bosons f0=0.425±0.166(stat)±0.102(syst) and the f…

Limits on anomalous trilinear gauge couplings fromWW→e+e−,WW→e±μ∓, andWW→μ+μ−events frompp¯collisions ats=1.96  TeV

Limits are set on anomalous WW gamma and WWZ trilinear gauge couplings using W+W--> e(+)nu(e)e(-)(nu) over bar (e), W+W--> e(+/-)nu(e)mu(-/+)nu(mu), and W+W-->mu(+)nu(mu)mu(-)(nu) over bar (mu) events. The data set was collected by the Run II D0 detector at the Fermilab Tevatron Collider and corresponds to approximately 250 pb(-1) of integrated luminosity at root s=1.96 TeV. Under the assumption that the WW gamma couplings are equal to the WWZ couplings and using a form factor scale of Lambda=2.0 TeV, the combined 95% C.L. one-dimensional coupling limits from all three channels are -0.32 <Delta kappa < 0.45 and -0.29 <lambda < 0.30.

Search for Neutral, Long-Lived Particles Decaying into Two Muons inpp¯Collisions ats=1.96  TeV

We present a search for a neutral particle, pair-produced in p-pbar collisions at sqrt(s)=1.96 TeV, which decays into two muons and lives long enough to travel at least 5 cm before decaying. The analysis uses ~380 pb^-1 of data recorded with the D0 detector. The background is estimated to be about one event. No candidates are observed, and limits are set on the pair production cross section times branching fraction into dimuons + X for such particles. For a mass of 10 GeV and lifetime of 4x10^-11 s, we exclude values greater than 0.14 pb (95% C.L.). These results are used to limit the interpretation of NuTeV's excess of di-muon events.

Measurement of the ttbar cross section using high-multiplicity jet events

We present a measurement of the ttbar cross section using high-multiplicity jet events produced in ppbar collisions at sqrt{s}=1.96 TeV. These data were recorded at the Fermilab Tevatron collider with the D0 detector. Events with at least six jets, two of them identified as b jets, were selected from a 1 fb-1 data set. The measured cross section, assuming a top quark mass of 175 GeV/c^2, is 6.9 \pm 2.0 pb, in agreement with theoretical expectations.

Double parton interactions inγ+3jet andγ+b/cjet+2jet events inpp¯collisions ats=1.96 TeV

We determine the fraction of events with double parton (DP) Scattering in a single p (p) over bar collisions at root s = 1.96 TeV in gamma + 3 jet and gamma + b/c jet + 2 jet events collected with the D0 detector and corresponding to an integrated luminosity of about 8.7 fb(-1). The DP fractions and effective cross sections (sigma(eff)) are measured for both event samples using the same kinematic selections. The measured DP fractions range from 0.21 to 0.17, with effective cross sections in the gamma + 3 jet and gamma + b/cjet + 2 jet samples of sigma(incl)(eff) = 12.7 +/- 0.2(stat) +/- 1.3(syst) mb and sigma(HF)(eff) = 14.6 +/- 0.6(stat) +/- 3.2(syst) mb, respectively.

Measurement of Semileptonic Branching Fractions ofBMesons to NarrowD**States

Using the data accumulated in 2002-2004 with the D0 detector in proton-antiproton collisions at the Fermilab Tevatron collider with a center-of-mass energy of 1.96 TeV, the branching fractions of the decays B ->(D) over bar (0)(1)(2420)mu(+)nu(mu)X and B ->(D) over bar (*0)(2)(2460)mu(+)nu(mu)X and their ratio have been measured: B (b) over bar -> B)xB(B -> (D) over bar (0)(1)mu(+)nu(mu)X)xB((D) over bar (0)(1)-> D(*-)pi(+))=[0.087 +/- 0.007(stat)+/- 0.014(syst)]%; B((b) over bar -> B)xB(B ->(D) over bar (*0)(2)mu(+)nu(mu)X)xB((D) over bar (*0)(2)-> D(*-)pi(+))=[0.035 +/- 0.007(stat)+/- 0.008(syst)]% and [B(B ->(D) over bar (*0)(2)mu(+)nu(mu)X)xB((D) over bar (*0)(2)-> D(*-)pi(+))]/[B(B ->(…

Search for Neutral Higgs Bosons Decaying to Tau Pairs inpp¯Collisions ats=1.96  TeV

A search for the production of neutral Higgs bosons {Phi} decaying into {tau}{sup +}{tau}{sup -} final states in p{bar p} collisions at a center-of-mass energy of 1.96 TeV is presented. The data, corresponding to an integrated luminosity of approximately 325 pb{sup -1}, were collected by the D0 experiment at the Fermilab Tevatron Collider. Since no excess compared to the expectation from standard model processes is found, limits on the production cross section times branching ratio are set. The results are combined with those obtained from the D0 search for {Phi}b({bar b}) {yields} b{bar b}b({bar b}) and are interpreted in the minimal supersymmetric standard model.

Search for scalar quarks in Z0 decays

A search has been made for pairs of scalar quarks (squarks) produced in e+e- annihilations at LEP (√s≃MZ0), and decaying into a standard quark and a neutral, non-interacting, stable, massive particle (the lightest supersymmetric particle, LSP). The search has been conducted for differences in the mass of the squark and LSP of 2 GeV/c2 and above. Up squarks with masses below 42 GeV/c2 and down squarks below 43 GeV/c2 were excluded. Six squark flavours degenerate in mass were excluded below 45 GeV/c2.

Multiplicity dependence of mean transverse momentum in $e^+e^-$ annihilations at LEP energies

A strong increase of the mean transverse momentum [p(t)] with the number of charged particles n(ch) is observed in e+e- annihilations into hadrons at LEP energies, The effect resembles correlations observed in hadron-hadron interactions. In e+e- annihilations the [p(t)] and n(ch) correlations can be accounted for by gluon radiation.

Measurement of top quark polarization in tt¯ lepton+jets final states

Department of Energy (USA); National Science Foundation (USA); Alternative Energies and Atomic Energy Commission and National Center for Scientific Research/National Institute of Nuclear and Particle Physics (France); Ministry of Education and Science of the Russian Federation (Russia); National Research Center "Kurchatov Institute" of the Russian Federation (Russia); Russian Foundation for Basic Research (Russia); Carlos Chagas Filho Foundation for the Support of Research in the State of Rio de Janeiro (Brazil); Department of Science and Technology (India); Administrative Department of Science, Technology and Innovation (Colombia); National Council of Science and Technology (Mexico); Natio…

Charged particle multiplicity distributions in restricted rapidity intervals in Z0 hadronic decays.

The multiplicity distributions of charged particles in restricted rapidity intervals in Z0 hadronic decays measured by the DELPHI detector are presented. The data reveal a shoulder structure, best visible for intervals of intermediate size, i.e. for rapidity limits around ±1.5. The whole set of distributions including the shoulder structure is reproduced by the Lund Parton Shower model. The structure is found to be due to important contributions from 3-and 4-jet events with a hard gluon jet. A different model, based on the concept of independently produced groups of particles, "clans", fluctuating both in number per event and particle content per clan, has also been used to analyse the pres…

Search for Diphoton Events with Large Missing Transverse Energy in6.3  fb−1ofpp¯Collisions ats=1.96  TeV

We report a search for diphoton events with large missing transverse energy produced in p (p) over bar collisions at root s = 1.96 TeV. The data were collected with the D0 detector at the Fermilab ...

Measurement of the forward-backward asymmetry inΛb0andΛ¯b0baryon production inpp¯collisions ats=1.96TeV

We measure the forward-backward asymmetry in the production of Lambda(0)(b) and (Lambda) over bar (0)(b) baryons as a function of rapidity in p (p) over bar collisions at root s = 1.96 TeV using 10.4 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron collider. The asymmetry is determined by the preference of Lambda(0)(b) or (Lambda) over bar (0)(b) particles to be produced in the direction of the beam protons or antiprotons, respectively. The measured asymmetry integrated over rapidity y in the range 0.1 < vertical bar y vertical bar < 2.0 is A = 0.04 +/- 0.07(stat) +/- 0.02(syst).

Measurement of the Electron Charge Asymmetry inpp¯→W+X→eν+XEvents ats=1.96  TeV

We present a measurement of the electron charge asymmetry in ppbar->W+X->enu+X events at a center of mass energy of 1.96 TeV using 0.75 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron transverse momentum and pseudorapidity in the interval (-3.2, 3.2) and is compared with expectations from next-to-leading order calculations in perturbative quantum chromodynamics. These measurements will allow more accurate determinations of the proton parton distribution functions.

Measurement of the top quark mass in the lepton+jets channel using the ideogram method

A measurement of the top quark mass using events with one charged lepton, missing transverse energy, and jets in the final state, collected by the D0 detector from p-pbar collisions at sqrt{s} = 1.96 TeV at the Fermilab Tevatron collider, is presented. A constrained fit is used to fully reconstruct the kinematics of the events. For every event a top quark mass likelihood is calculated taking into account all possible jet assignments and the probability that an event is signal or background. Lifetime-based identification of b jets is employed to enhance the separation between t-tbar signal and background from other physics processes and to improve the assignment of the observed jets to the q…

Search for neutral supersymmetric higgs bosons in multijet events at s=1.96TeV

Made available in DSpace on 2022-04-28T20:06:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-10-07 We have performed a search for neutral Higgs bosons produced in association with bottom quarks in pp collisions, using 260pb-1 of data collected with the D0 detector in Run II of the Fermilab Tevatron Collider. The cross sections for these processes are enhanced in many extensions of the standard model (SM), such as in its minimal supersymmetric extension at large tanâ□¡Î. The results of our analysis agree with expectations from the SM, and we use our measurements to set upper limits on the production of neutral Higgs bosons in the mass range of 90 to 150 GeV. © 2005 The American Ph…

Simultaneous measurement of forward-backward asymmetry and top polarization in dilepton final states fromtt¯production at the Tevatron

We present a simultaneous measurement of the forward-backward asymmetry and the top-quark polarization in t (t) over bar production in dilepton final states using 9.7 fb(-1) of proton-antiproton collisions at root s = 1.96 TeV with the D0 detector. To reconstruct the distributions of kinematic observables we employ a matrix element technique that calculates the likelihood of the possible t (t) over bar kinematic configurations. After accounting for the presence of background events and for calibration effects, we obtain a forward-backward asymmetry of A(t (t) over bar) = (15.0 +/- 6.4(stat) +/- 4.9(syst)) % and a top-quark polarization times spin analyzing power in the beam basis of kappa P…

Measurement of B(t→Wb)/B(t→Wq) at s=1.96TeV

We present the measurement of R = B(t -> Wb)/B(t -> Wq) in pp collisions at root s = 1.96 TeV, using 230 pb(-1) of data collected by the DO experiment at the Fermilab Tevatron Collider. We fit simultaneously R and the number (N-tt) of selected top quark pairs (tt), to the number of identified b-quark jets in events with one electron or one muon, three or more jets, and high transverse energy imbalance. To improve sensitivity, kinematical properties of events with no identified b-quark jets are included in the fit. We measure R = 1.03(-0.17)(0.19) (stat + syst), in good agreement with the standard model. We set lower limits of R > 0.61 and vertical bar V-tb vertical bar > 0.78 at 95% confide…

Combined Forward-Backward Asymmetry Measurements in Top-Antitop Quark Production at the Tevatron

The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of √s=1.96  TeV. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is At¯tFB=0.128±0.025. The combined inclusive and differential asymmetries are consistent with recent standard model predictions.

Search for Randall-Sundrum gravitons in dilepton and diphoton final states

We report the first direct search for the Kaluza-Klein (KK) modes of Randall-Sundrum gravitons using dielectron, dimuon, and diphoton events observed with the D0 detector operating at the Fermilab Tevatron ppbar Collider at sqrt(s) = 1.96 TeV. No evidence for resonant production of gravitons has been found in the data corresponding to an integrated luminosity of approximately 260 pb^-1. Lower limits on the mass of the first KK mode at the 95% C.L. have been set between 250 and 785 GeV, depending on its coupling to SM particles.

Search for Heavy Particles Decaying into Electron-Positron Pairs inpp¯Collisions

We present results of searches for technirho (rho (T)), techniomega (omega (T)), and Z' particles, using the decay channels rho (T), omega (T), Z' --> e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the DO detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes p (p) over bar --> rho (T), omega (T), Z' - e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho (T) and omega (T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermi…

Search for associated production of charginos and neutralinos in the trilepton final state using 2.3 fb-1 of data

We report the results of a search for associated production of charginos and neutralinos using a data set corresponding to an integrated luminosity of 2.3 fb-1 collected with the D0 experiment during Run II of the Tevatron proton-antiproton collider. Final states containing three charged leptons and missing transverse energy are probed for a signal from supersymmetry with four dedicated trilepton event selections. No evidence for a signal is observed, and we set limits on the product of production cross section and leptonic branching fraction. Within minimal supergravity, these limits translate into bounds on m_0 and m_1/2 that are well beyond existing limits.

Measurement of the ratio of three-jet to two-jet cross sections in pp¯ collisions at s=1.96 TeV

We present a measurement of the ratio of multijet cross sections in pp-bar collisions at sqrt(s) = 1.96 TeV at the Fermilab Tevatron Collider. The measurement is based on a data set corresponding to an integrated luminosity of 0.7 fb-1 collected with the D0 detector. The ratio of the inclusive three-jet to two-jet cross sections, R3/2, has been measured as a function of the jet transverse momenta. The data are compared to QCD predictions in different approximations. Popular tunes of the PYTHIA event generator do not agree with the data, while SHERPA provides a reasonable description of the data. A perturbative QCD prediction in next-to-leading order in the strong coupling constant, correcte…

Bounds on an Anomalous Dijet Resonance inW+jetsProduction inpp¯Collisions ats=1.96  TeV

We present a study of the dijet invariant mass spectrum in events with two jets produced in association with a $W$ boson in data corresponding to an integrated luminosity of 4.3 fb$^{-1}$ collected with the D0 detector at $\sqrt{s} =1.96$ TeV. We find no evidence for anomalous resonant dijet production and derive upper limits on the production cross section of an anomalous dijet resonance recently reported by the CDF Collaboration, investigating the range of dijet invariant mass from 110 to 170 GeV/$c^2$. The probability of the D0 data being consistent with the presence of a dijet resonance with 4 pb production cross section at 145 GeV/$c^2$ is $8\times 10^{-6}$.

Determination of 55-155-155-1in second order QCD from hadronic Z decays

Distributions of event shape variables obtained from 120600 hadronic Z decays measured with the DELPHI detector are compared to the predictions of QCD based event generators. Values of the strong coupling constant αs are derived as a function of the renormalization scale from a quantitative analysis of eight hadronic distributions. The final result, αs(MZ), is based on second order perturbation theory and uses two hadronization corrections, one computed with a parton shower model and the other with a QCD matrix element model. © 1992 Springer-Verlag.

Measurement of inclusive ρ0, f0(980), f2(1270), K and f′2(1525) production in Z0 decays

DELPHI results are presented on the inclusive production of the neutral mesons ρ0, f0(980), f2(1270), KView the MathML source and f′2(1525) in hadronic Z0 decays. They are based on about 2 million multihadronic events collected in 1994 and 1995, using the particle identification capabilities of the DELPHI Ring Imaging Cherenkov detectors and measured ionization losses in the Time Projection Chamber. The total production rates per hadronic Z0 decay have been determined to be: 1.19±0.10 for ρ0; 0.164±0.021 for f0(980); 0.214±0.038 for f2(1270); 0.073±0.023 for KView the MathML source; and 0.012±0.006 for f′2(1525). The total production rates for all mesons and differential cross-sections for …

Search for flavor changing neutral currents via quark–gluon couplings in single top quark production using 2.3 fb−1 of pp¯ collisions

We present a search for flavor changing neutral currents via quark-gluon couplings in a sample of single top quark final states corresponding to 2.3 fb(-1) of integrated luminosity collected with the DO detector at the Fermilab Tevatron Collider. We select events containing a single top quark candidates with an additional jet, and obtain separation between signal and background using Bayesian neural networks. We find consistency between background expectation and observed data, and set limits on flavor changing neutral current gluon couplings of the top quark to up quarks (tgu) and charm quarks (tgc). The cross section limits at the 95% C.L. are sigma(tgu) gu) gc) < 3.9 x 10(-3).

Measurement of the dijet invariant mass cross section in pp¯ collisions at s=1.96 TeV

The inclusive dijet production double differential cross section as a function of the dijet invariant mass and of the largest absolute rapidity (y_{max}) of the two jets with the largest transverse momentum in an event is measured in proton anti-proton collisions at sqrt{s} = 1.96$ TeV using 0.7 fb^{-1} of data collected with the D0 detector at the Fermilab Tevatron Collider. The measurement is performed in six rapidity regions up to |y|=2.4. Next-to-leading order perturbative QCD predictions are found to be in agreement with the data.

Lifetime and production rate of beauty baryons from Z decays

The production and decay of beauty baryons (b-baryons) have been studied using 1.7 \times 10^6 Z hadronic decays collected by the DELPHI detector at LEP. Three different techniques were used to identify the b-baryons. The first method used pairs of a \Lambda and a lepton to tag the b-baryon decay. The second method associated fully reconstructed \Lambda_c baryons with leptons. The third analysis reconstructed the b-baryon decay points by forming secondary vertices from identified protons and muons of opposite sign. Using these methods the following production rates were measured: \begin{eqnarray*} f(\qb \ra \Bb) \times \BR(\Bb \ra \mLs \ell\bar{\nu}_{\ell}\X) & = & (0.30 \pm 0.06 \pm0.04)\%…

Search for Doubly Charged Higgs Boson Pair Production in the Decay toμ+μ+μ−μ−inpp¯Collisions ats=1.96  TeV

A search for pair production of doubly charged Higgs bosons in the process p (p) over bar -->H++H---->mu(+)mu(+)mu(-)mu(-) is performed with the D0 run II detector at the Fermilab Tevatron. The analysis is based on a sample of inclusive dimuon data collected at an energy of roots=1.96 TeV, corresponding to an integrated luminosity of 113 pb(-1). In the absence of a signal, 95% confidence level mass limits of M(H-L(+/-+/-))>118.4 GeV/c(2) and M(H-R(+/-+/-))>98.2 GeV/c(2) are set for left-handed and right-handed doubly charged Higgs bosons, respectively, assuming 100% branching into muon pairs.

Experimental Discrimination between Charge2e/3Top Quark and Charge4e/3Exotic Quark Production Scenarios

We present the first experimental discrimination between the 2e/3 and 4e/3 top quark electric charge scenarios, using top quark pairs (ttbar) produced in ppbar collisions at sqrt{s}=1.96 TeV by the Fermilab Tevatron collider. We use 370 pb-1 of data collected by the D0 experiment and select events with at least one high transverse momentum electron or muon, high transverse energy imbalance, and four or more jets. We discriminate between b- and bbar-quark jets by using the charge and momenta of tracks within the jet cones. The data is consistent with the expected electric charge, |q|=2e/3. We exclude, at the 92% C.L., that the sample is solely due to the production of exotic quark pairs QQba…

Measurement of the Semileptonic Charge Asymmetry usingBs0→DsμXDecays

We present a measurement of the time-integrated flavor-specific semileptonic charge asymmetry in the decays of B{sub s}{sup 0} mesons that have undergone flavor mixing, a{sub sl}{sup s}, using B{sub s}{sup 0} ({bar B}{sub s}{sup 0}) {yields} D{sub s}{sup {-+}} {mu}{sup {+-}} X decays, with D{sub s}{sup {-+}} {yields} {phi}{pi}{sup {-+}} and {phi} {yields} K{sup +}K{sup -}, using 10.4 fb{sup -1} of proton-antiproton collisions collected by the D0 detector during Run II at the Fermilab Tevatron Collider. A fit to the difference between the time-integrated D{sub s}{sup -} and D{sub s}{sup +} mass distributions of the B{sub s}{sup 0} and {bar B}{sub s}{sup 0} candidates yields the flavor-specif…

Measurement of the differential cross sectiondσ/dtin elasticpp¯scattering ats=1.96  TeV

We present a measurement of the elastic differential cross section $d\sigma(p\bar{p}\rightarrow p\bar{p})/dt$ as a function of the four-momentum-transfer squared t. The data sample corresponds to an integrated luminosity of $\approx 31 nb^{-1}$ collected with the D0 detector using dedicated Tevatron $p\bar{p} $ Collider operating conditions at sqrt(s) = 1.96 TeV and covers the range $0.26 <|t|< 1.2 GeV^2$. For $|t|<0.6 GeV^2$, d\sigma/dt is described by an exponential function of the form $Ae^{-b|t|}$ with a slope parameter $ b = 16.86 \pm 0.10(stat) \pm 0.20(syst) GeV^{-2}$. A change in slope is observed at $|t| \approx 0.6 GeV^2$, followed by a more gradual |t| dependence with increasing …

Search for neutral Higgs bosons in the multi-b-jet topology in 5.2 fb−1 of pp¯ collisions at s=1.96 TeV

Data recorded by the D0 experiment at the Fermilab Tevatron Collider are analyzed to search for neutral Higgs bosons produced in association with b quarks. The search is performed in the three-b-quark channel using multijet-triggered events corresponding to an integrated luminosity of 5.2fb-1. In the absence of any significant excess above background, limits are set on the cross section multiplied by the branching ratio in the Higgs boson mass range 90 to 300 GeV, extending the excluded regions in the parameter space of the minimal supersymmetric standard model.

ZZ→l+l−νν¯production inpp¯collisions ats=1.96  TeV

We describe a search for Z boson pair production in pp collisions at sqrt(s)= 1.96 TeV with the D0 detector at the Fermilab Tevatron Collider using a data sample corresponding to an integrated luminosity of 2.7 fb^-1. Using the final state decay ZZ to llvv (where l = e or mu) we measure a signal with a 2.6 standard deviations significance (2.0 expected) and measure a cross section of sigma(pp to ZZ + X) = 2.01 +- 0.93 (stat.) +- 0.29 (sys.) pb.

Measurement of theWboson helicity in top quark decays using5.4  fb−1ofpp¯collision data

We present a measurement of the helicity of the W boson produced in top quark decays using t{bar t} decays in the {ell}+jets and dilepton final states selected from a sample of 5.4 fb{sup -1} of collisions recorded using the D0 detector at the Fermilab Tevatron p{bar p} collider. We measure the fractions of longitudinal and right-handed W bosons to be f{sub 0} = 0.669 {+-} 0.102 [{+-}0.078 (stat.) {+-} 0.065 (syst.)] and f{sub +} = 0.023 {+-} 0.053 [{+-}0.041 (stat.){+-}0.034 (syst.)], respectively. This result is consistent at the 98% level with the standard model. A measurement with f{sub 0} fixed to the value from the standard model yields f{sub +} = 0.010 {+-} 0.037 [{+-}0.022 (stat.) {…

Search for charged Higgs bosons in e^{+}e^{-}$ collisions at √s=172 GeV

This paper presents results on charged Higgs boson production, based on LEP data collected at √s = 172 GeV, that complement the previous DELPHI results obtained at centre of mass energies up to 161 GeV. The charged Higgs bosons are assumed to be pair produced and to decay either into a quark pair or into τVτ. The three different possible final states are included in the analysis. Data from ring imaging Cherenkov and microvertex detectors are used to identify the quarks as a cs pair. The number of candidates found is compatible with the background expected from standard processes. Combining the results of the present analysis with those of the previous analysis at lower energies, a new lower…

Measurement of the partial width of the decay of the Z0 into charm quark pairs

A determination of the partial width Γc̄ of the Z0 boson into charm quark pairs is presented, based on a total sample of 36 900 Z0 hadronic decays measured with the DELPHI detector at the LEP collider. The production rate of cc events is derived from the inclusive analysis of charged pions coming from the decay of charmed meson D*+-→D0π+ and D*-→D̄0π- where the π± is constrained by kinematics to have a low pT with respect to the jet axis. The probability to procedure these π± from D*± decay in cc events is taken to be 0.31±0.05 as measured at √S = 10.55 GeV. The measured relative partial width Γ∞/Γh = 0.162± 0.030(stat.) ± 0.050(syst.) is in good agreement with the standard model value of 0…

Measurement of Dijet Angular Distributions ats=1.96  TeVand Searches for Quark Compositeness and Extra Spatial Dimensions

We present the first measurement of dijet angular distributions in ppbar collisions at sqrt{s}=1.96TeV at the Fermilab Tevatron Collider. The measurement is based on a dataset corresponding to an integrated luminosity of up to 0.7fb-1 collected with the D0 detector. Dijet angular distributions have been measured over a range of dijet masses, from 0.25TeV to above 1.1TeV. The data are in good agreement with the predictions of perturbative QCD and are used to constrain new physics models including quark compositeness, large extra dimensions, and TeV-1 scale extra dimensions. For all models we set the most stringent direct limits to date.

Observation of Single Top Quark Production

We report observation of the electroweak production of single top quarks in ppbar collisions at sqrt(s) = 1.96 TeV based on 2.3 fb^-1 of data collected by the D0 detector at the Fermilab Tevatron Collider. Using events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks, we measure a cross section of sigma(ppbar -&gt; tb + X, tqb + X) = 3.94 +- 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5 x 10^-7, corresponding to a 5.0 standard deviation significance for the observation.

Properties ofL=1B1andB2*Mesons

This Letter presents the first strong evidence for the resolution of the excited B mesons B-1 and B-2(*) as two separate states in fully reconstructed decays to B+(*())pi(-). The mass of B-1 is measured to be 5720.6 +/- 2.4 +/- 1.4 MeV/c(2) and the mass difference Delta M between B-2* and B-1 is 26.2 +/- 3.1 +/- 0: 9 MeV/c(2), giving the mass of the B-2* as 5746.8 +/- 2.4 +/- 1.7 MeV/c(2). The production rate for B-1 and B-2* mesons is determined to be a fraction (13.9 +/- 1.9 +/- 3.2)% of the production rate of the B+ meson.

MEASUREMENT OF THE FORWARD-BACKWARD ASYMMETRY OF CHARM AND BOTTOM QUARKS AT THE Z-POLE USING D-ASTERISK(+/-)-MESONS

The forward-backward asymmetries for the processes $$e^ + e^ - \to c\bar c$$ and $$e^ + e^ - \to b\bar b$$ at theZ resonance are measured using identifiedD *± mesons. In 905,000 selected hadronic events, taken in 1991 and 1992 with the DEL-PHI detector at LEP, 4757D *+→D 0π+ decays are reconstructed. Thec andb quark forward-backward asymmetries are determined to be: $$\begin{gathered} A_{FB}^{c\bar c} = 0.077 \pm 0.029(stat) \pm 0.012(sys), \hfill \\ A_{FB}^{b\bar b} = 0.059 \pm 0.062(stat) \pm 0.024(sys). \hfill \\ \end{gathered} $$ Constraining theb asymmetry to the value measured by DELPHI using independent analyses, the charm asymmetry is determined to be: $$A_{FB}^{c,const} = 0.068 \pm…

Measurement of the top quark mass in final states with two leptons

We present measurements of the top quark mass in ttbar candidate events with two final state leptons using 1 inverse fb of data collected by the D0 experiment. Our data sample is selected by requiring two fully identified leptons or by relaxing one lepton requirement to an isolated track if at least one jet is tagged as a b jet. The top quark mass is extracted after reconstructing the event kinematics under the ttbar hypothesis using two methods. In the first method, we integrate over expected neutrino rapidity distributions, and in the second we calculate a weight for the possible top quark masses based on the observed particle momenta and the known parton distribution functions. We analyz…

Search for resonant diphoton production with the D0 detector

We present a search for a narrow resonance in the inclusive diphoton final state using 2.7 fb-1 of data collected with the D0 detector at the Fermilab Tevatron ppbar Collider. We observe good agreement between the data and the background prediction, and set the first 95% C.L. upper limits on the production cross section times the branching ratio for decay into a pair of photons for resonance masses between 100 and 150 GeV. This search is also interpreted in the context of several models of electroweak symmetry breaking with a Higgs boson decaying into two photons.

Search for a heavy neutral gauge boson in the dielectron channel with 5.4 fb−1 of pp¯ collisions at s=1.96 TeV

We report the results of a search for a heavy neutral gauge boson Z' decaying into the dielectron final state using data corresponding to an integrated luminosity of 5.4 fb(-1) collected by the D0 experiment at the Fermilab Tevatron Collider. No significant excess above the standard model prediction is observed in the dielectron invariant-mass spectrum. We set 95 sigma(p (p) over bar -> Z') x BR(Z' -> ee) depending on the dielectron invariant mass. These cross section limits are used to determine lower mass limits for bosons in a variety of models. For the sequential standard model boson a lower mass limit of 1023 GeV is obtained.

Search for minimal supergravity in single-electron events with jets and large missing transverse energy inpp¯collisions ats=1.8TeV

We describe a search for evidence of minimal supergravity (MSUGRA) in 92.7 pb(-1) of data collected with the D empty set detector at the Fermilab Tevatron p (p) over bar collider at roots=1.8 TeV. Events with a single electron, four or more jets, and large missing transverse energy were used in this search. The major backgrounds are from W+jets, misidentified multijet, t (t) over bar, and WW production. We observe no excess above the expected number of background events in our data. A new limit in terms of MSUGRA model parameters is obtained.

Observation of theBcMeson in the Exclusive DecayBc→J/ψπ

A fully reconstructed B-c -> J/psi pi signal is observed with the D0 detector at the Fermilab Tevatron p (p) over bar collider using 1.3 fb(-1) of integrated luminosity. The signal consists of 54 +/- 12 candidates with a significance that exceeds 5 standard deviations, and confirms earlier observations of this decay. The measured mass of the B-c meson is 6300 +/- 14(stat)+/- 5(syst) MeV/c(2).

Measurement of Z/γ∗+jet+X angular distributions in pp¯ collisions at s=1.96 TeV

We present the first measurements at a hadron collider of differential cross sections for Z+jet+X production in delta phi(Z, jet), |delta y(Z, jet)| and |y_boost(Z, jet)|. Vector boson production in association with jets is an excellent probe of QCD and constitutes the main background to many small cross section processes, such as associated Higgs production. These measurements are crucial tests of the predictions of perturbative QCD and current event generators, which have varied success in describing the data. Using these measurements as inputs in tuning event generators will increase the experimental sensitivity to rare signals.

First measurement of the forward-backward charge asymmetry in top quark pair production

We present the first measurement of the integrated forward-backward charge asymmetry in top-antitop quark pair (ttbar) production in proton-antiproton collisions in the lepton plus jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming ttbar+X production and decay, a sample of 0.9fb-1 of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on ttbar+X production via a Z' resonance.

mb at MZ

Abstract The value of the b quark mass at the M Z scale defined in the MS renormalization scheme, m b ( M Z ), was determined using 2.8 million hadronic Z decays collected during 1992-1994 by the DELPHI detector to be m b (M Z )=2.67±0.25 ( stat. )±0.34 ( frag. )±0.27 ( theo. ) GeV/c 2 . The analysis considers NLO corrections to the three-jet production rate including mass effects, and the result obtained agrees with the QCD prediction of having a running b quark mass at an energy scale equal to M Z . This is the first time that such a measurement is performed far above the b b production threshold. The study also verifies the flavour independence of the strong coupling constant for b and l…

A measurement of the photon structure function F-2(gamma) at an average Q(2) of 12 GeV2/c(4)

The hadronic photon structure function F_{2}^{gamma} has been measured in the Q^{2} range from 4 to 30~GeV^2/c^{4} and down to x values of order 0.001, using data taken with the DELPHI detector at LEP between 1991 and 1993. A comparison is made with several F_{2}^{gamma} parameterizations with special emphasis on their low x behaviour. A result on the Q^{2} evolution of F_{2}^{gamma} is presented.

Measurement ofsin2θeffℓandZ-light quark couplings using the forward-backward charge asymmetry inpp¯→Z/γ*→e+e−events withL=5.0  fb−1ats=1.96  TeV

We measure the mass dependence of the forward-backward charge asymmetry in 157,553 $p\bar{p} \rightarrow Z/\gamma^{*} \rightarrow e^+e^-$ interactions, corresponding to 5.0 fb$^{-1}$ of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider at $\sqrt{s}=1.96$ TeV. The effective weak mixing angle ($\sin^2\theta_{eff}^{lept}$) from this process involving predominantly the first generation of quarks is extracted as $\sin^2\theta_{eff}^{lept} = 0.2309 \pm 0.0008 ({stat.}) \pm 0.0006 ({syst.})$. We also present the most precise direct measurement of the vector and axial-vector couplings of $u$ and $d$ quarks to the $Z$ boson.

Search for scalar leptoquarks from Z$^0$ decays

We have searched for pair produced scalar leptoquarks each decaying to a quark and a charged lepton in a sample of 116 000 hadronic Z0 events produced at LEP. No candidate was detected and cross section and branching ratio limits are set for the above process at 95% CL. Mass limits are found to be about 42 GeV/c2 depending only slightly on the models used and a coupling times branching ratio exclusion line is drawn for a scalar leptoquark with a free coupling. We have also probed the mass region above 45 GeV/c2 for a singly produced scalar leptoquark and set limits on the cross section and the coupling lambda(2)/4-pi up to 60 GeV.

MEASUREMENT OF THE GAMMA(B-B-OVER-BAR)/GAMMA(HAD) BRANCHING RATIO OF THE Z BY DOUBLE HEMISPHERE TAGGING

Two measurements of {Mathematical expression} are presented. Both measurements use 250000 Z decays taken with the DELPHI detector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results, {Mathematical expression} is found to be 0.2209±0.0041(stat.)±0.0042(syst.)±0.0018 {Mathematical expression}. © 1995 Springer-Verlag.

Search for W′→tb resonances with left- and right-handed couplings to fermions

We present a search for the production of a heavy gauge boson, W', that decays to third-generation quarks, by the D0 Collaboration in ppbar collisions at sqrt(s)= 1.96 TeV. We set 95% confidence level upper limits on the production cross section times branching fraction. For the first time, we set limits for arbitrary combinations of left- and right-handed couplings of the W' boson to fermions. For couplings with the same strength as the standard model W boson, we set the following limits for M(W') > m(nu_R): M(W')>863 GeV for purely left-handed couplings, M(W')>885 GeV for purely right-handed couplings, and M(W')>916 GeV if both left- and right-handed couplings are present. The limit for r…

b-Jet identification in the D0 experiment

Algorithms distinguishing jets originating from b quarks from other jet flavors are important tools in the physics program of the D0 experiment at the Fermilab Tevatron p-pbar collider. This article describes the methods that have been used to identify b-quark jets, exploiting in particular the long lifetimes of b-flavored hadrons, and the calibration of the performance of these algorithms based on collider data.

Search for charged massive long-lived particles ats=1.96  TeV

We present a search for charged massive long-lived particles (CMLLPs) that are pair produced in p-pbar collisions at sqrt(s)= 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider. Our result is a combination of two searches where either one or both CMLLPs are reconstructed in the detector. We select events with muon-like particles that have both speed and ionization energy loss dE/dx different from muons produced in p-pbar collisions. In the absence of evidence for CMLLPs corresponding to 6.3 fb-1 of integrated luminosity, we set limits on the CMLLP masses in several supersymmetric models, excluding masses below 278 GeV for long-lived gaugino-like charginos, and masses …

Search for single top quarks in the tau + jets channel using 4.8 fb−1 of pp¯ collision data

We present the first direct search for single top quark production using tau leptons. The search is based on 4.8 fb$^{-1}$ of integrated luminosity collected in $p\bar{p}$ collisions at $\sqrt{s}$=1.96 TeV with the D0 detector at the Fermilab Tevatron Collider. We select events with a final state including an isolated tau lepton, missing transverse energy, two or three jets, one or two of them $b$ tagged. We use a multivariate technique to discriminate signal from background. The number of events observed in data in this final state is consistent with the signal plus background expectation. We set in the tau+jets channel an upper limit on the single top quark cross section of \TauLimObs pb …

Measurement of the Inclusive Jet Cross Section inpp¯Collisions ats=1.96  TeV

We report on a measurement of the inclusive jet cross section in p (p) over bar collisions at a center-of-mass energy root s = 1.96 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider corresponding to an integrated luminosity of 0: 70 fb(-1). The data cover jet transverse momenta from 50 to 600 GeV and jet rapidities in the range -2.4 to 2.4. Detailed studies of correlations between systematic uncertainties in transverse momentum and rapidity are presented, and the cross section measurements are found to be in good agreement with next-to-leading order QCD calculations.

Evidence for production of single top quarks and first direct measurement of |Vtb|.

The D0 Collaboration presents first evidence for the production of single top quarks at the Fermilab Tevatron ppbar collider. Using a 0.9 fb^-1 dataset, we apply a multivariate analysis to separate signal from background and measure sigma(ppbar-&gt;tb+X,tqb+X) = 4.9 +- 1.4 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.035%, corresponding to a 3.4 standard deviation significance. We use the cross section measurement to directly determine the CKM matrix element that describes the Wtb coupling and find 0.68 &lt; |Vtb| &lt;= 1 at 95% C.L. within the standard model.

Evidence for aBs0π±State

Made available in DSpace on 2022-04-28T19:03:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-07-07 We report evidence for a narrow structure, X(5568), in the decay sequence X(5568)→Bs0π±, Bs0→J/ψφ, J/ψ→μ+μ-, φ→K+K-. This is evidence for the first instance of a hadronic state with valence quarks of four different flavors. The mass and natural width of this state are measured to be m=5567.8±2.9(stat)-1.9+0.9(syst) MeV/c2 and Γ=21.9±6.4(stat)-2.5+5.0(syst) MeV/c2. If the decay is X(5568)→Bs∗π±→Bs0γπ± with an unseen γ, m(X(5568)) will be shifted up by m(Bs∗)-m(Bs0)∼49 MeV/c2. This measurement is based on 10.4 fb-1 of pp collision data at s=1.96 TeV collected by the D0 experiment at th…