0000000001047915
AUTHOR
Andrey Korytov
Search for a Standard Model Higgs Boson inWH→ℓvbb¯inpp¯Collisions ats=1.96 TeV
We present a search for a standard model Higgs boson produced in association with a W boson using 2.7 fb(-1) of integrated luminosity of pp collision data taken at square root s = 1.96 TeV. Limits on the Higgs boson production rate are obtained for masses between 100 and 150 GeV/c(2). Through the use of multivariate techniques, the analysis achieves an observed (expected) 95% confidence level upper limit of 5.6 (4.8) times the theoretically expected production cross section for a standard model Higgs boson with a mass of 115 GeV/c(2).
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.
Search for Pair Production of Supersymmetric Top Quarks in Dilepton Events frompp¯Collisions ats=1.96 TeV
We present the results of a search for pair production of the supersymmetric partner of the top quark (the top squark (t) over tilde (1)) decaying to a b quark and a chargino (chi) over tilde (+/-)(1) with a subsequent (chi) over tilde (+/-)(1) decay into a neutralino (chi) over tilde (0)(1), lepton l, and neutrino nu Using a data sample corresponding to 2.7 fb(-1) of integrated luminosity of p (p) over bar collisions at root s = 1: 96 TeV collected by the CDF II detector, we reconstruct the mass of top squark candidate events and fit the observed mass spectrum to a combination of standard model processes and (t) over tilde (1)(t) over tilde (1). We find no evidence for (t) over tilde (1)(t…
Direct Measurement of theWProduction Charge Asymmetry inpp¯Collisions ats=1.96 TeV
We wish to thank R.S. Thorne and W.J. Stirling for useful discussions on the theoretical predictions.We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions. This work was supported by the U.S. Department of Energy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Foundation; the A.P. Sloan Foundation; the Bundesministerium fur Bildung und Forschung, Germany; the Korean Science…
Search for Technicolor Particles Produced in Association with a W Boson at CDF
7 páginas, 3 figuras, 1 tabla.-- PACS numbers: 14.80.Tt, 12.60.Nz, 13.85.Rm.-- CDF Collaboration: et al.
Updated Search for the Flavor-Changing Neutral-Current Decay D^0 \to {\mu} + {\mu}-
We report on a search for the flavor-changing neutral-current decay D0 \to {\mu}+ {\mu}- in pp collisions at \surd s = 1.96 TeV using 360 pb-1 of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. A displaced vertex trigger selects long-lived D0 candidates in the {\mu}+ {\mu}-, {\pi}+{\pi}-, and K-{\pi}+ decay modes. We use the Cabibbo-favored D0 \to K-{\pi}+ channel to optimize the selection criteria in an unbiased manner, and the kinematically similar D0 \to{\pi}+ {\pi}- channel for normalization. We set an upper limit on the branching fraction (D0 --> {\mu}+ {\mu}-) < 2.1 E-7 (3.0 E-7) at the 90% (95%) confidence level.
Direct Bound on the Total Decay Width of the Top Quark inpp¯Collisions ats=1.96 TeV
We present the first direct experimental bound on the total decay width of the top quark, Gamma(t), using 955 pb(-1) of the Tevatron's p (p) over bar collisions recorded by the Collider Detector at Fermilab. We identify 253 top-antitop pair candidate events. The distribution of reconstructed top quark mass from these events is fitted to templates representing different values of the top quark width. Using a confidence interval based on likelihood-ratio ordering, we extract an upper limit at 95% C.L. of Gamma(t) < 13.1 GeV for an assumed top quark mass of 175 GeV/c(2).
Search for new physics inlepton+photon+Xevents with929 pb−1ofpp¯collisions ats=1.96 TeV
The authors present results of a search for anomalous production of events containing a charged lepton ({ell}, either e or {mu}) and a photon ({gamma}), both with high transverse momentum, accompanied by additional signatures, X, including missing transverse energy (E{sub T}) and additional leptons and photons. We use the same kinematic selection criteria as in a previous CDF search, but with a substantially larger data set, 305 pb{sup -1}, a p{bar p} collision energy of 1.96 TeV, and the upgraded CDF II detector. We find 42 {ell}{gamma}E{sub T} events versus a standard model expectation of 37.3 {+-} 5.4 events. The level of excess observed in Run I, 16 events with an expectation of 7.6 {+-…
Search for High-Masse+e−Resonances inpp¯Collisions ats=1.96 TeV
We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions. This work was supported by the U.S. Department of Energy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Foundation; the A.P. Sloan Foundation; the Bundesministerium fur Bildung und Forschung, Germany; the Korean Science and Engineering Foundation and the Korean Research Foundation; the Science and Technology Facilities…
Search forWWandWZResonances Decaying to Electron, MissingET, and Two Jets inpp¯Collisions ats=1.96 TeV.
We present a search for WW and WZ production in final states that contain a charged lepton (electron or muon) and at least two jets, produced in {radical}(s)=1.96 TeV pp collisions at the Fermilab Tevatron, using data corresponding to 1.2 fb{sup -1} of integrated luminosity collected with the CDF II detector. Diboson production in this decay channel has yet to be observed at hadron colliders due to the large single W plus jets background. An artificial neural network has been developed to increase signal sensitivity, as compared with an event selection based on conventional cuts. We set a 95% confidence level upper limit of {sigma}{sub WW}xBR(W{yields}l{nu}{sub l},W{yields}jets)+{sigma}{sub…
Production ofψ(2S)mesons inpp¯collisions at 1.96 TeV
We have measured the differential cross section for the inclusive production of $\ensuremath{\psi}(2\mathrm{S})$ mesons decaying to ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ that were produced in prompt or $B$-decay processes from $p\overline{p}$ collisions at 1.96 TeV. These measurements have been made using a data set from an integrated luminosity of $1.1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ collected by the CDF II detector at Fermilab. For events with transverse momentum ${p}_{T}(\ensuremath{\psi}(2\mathrm{S}))g2\text{ }\text{ }\mathrm{GeV}/c$ and rapidity $|y(\ensuremath{\psi}(2\mathrm{S}))|l0.6$ we measure the integrated inclusive cross section $\ensuremath…
Search for single top quark production inpp¯collisions ats=1.96 TeVin the missing transverse energy plus jets topology
We report a search for single top quark production with the CDF II detector using 2.1 fb{sup -1} of integrated luminosity of pp collisions at {radical}(s)=1.96 TeV. The data selected consist of events characterized by large energy imbalance in the transverse plane and hadronic jets, and no identified electrons and muons, so the sample is enriched in W{yields}{tau}{nu} decays. In order to suppress backgrounds, additional kinematic and topological requirements are imposed through a neural network, and at least one of the jets must be identified as a b quark jet. We measure an excess of signal-like events in agreement with the standard model prediction, but inconsistent with a model without si…
Measurement of theb-hadron production cross section using decays toμ−D0Xfinal states inpp¯collisions ats=1.96 TeV
We report a measurement of the production cross section for b hadrons in p{bar p} collisions at {radical}s = 1.96 TeV. Using a data sample derived from an integrated luminosity 83 pb{sup -1} collected with the upgraded Collider Detector (CDF II) at the Fermilab Tevatron, we analyze b hadrons, H{sub b}, partially reconstructed in the semileptonic decay mode H{sub b} {yields} {mu}{sup -} D{sup 0} X. Our measurement of the inclusive production cross section for b hadrons with transverse momentum p{sub T} > 9 GeV/c and rapidity |y| < 0.6 is {sigma} = 1.30 {micro}b {+-} 0.05 {micro}b(stat) {+-} 0.14 {micro}b(syst) {+-} 0.07 {micro}b({Beta}), where the uncertainties are statistical, systematic, a…
Search forR-Parity Violating Decays of Sneutrinos toeμ,μτ, andeτPairs inpp¯Collisions ats=1.96 TeV
7 paginas, 2 figuras, 3 tablas.-- PACS numbers: 14.80.Ly, 12.60.Jv, 13.85.Qk, 14.60.St.--CDF Collaboration: et al.
Measurement of the fraction oftt¯production via gluon-gluon fusion inpp¯collisions ats=1.96 TeV
We present a measurement of the ratio of the tt production cross section via gluon-gluon fusion to the total tt production cross section in pp collisions at √s=1.96 TeV at the Tevatron. Using a data sample with an integrated luminosity of 955 pb-1 recorded by the CDF II detector at Fermilab, we select events based on the tt decay to lepton+jets. Using an artificial neural network technique we discriminate between tt events produced via qq annihilation and gg fusion, and find Gf=σ(gg→tt )/σ(pp →tt )<0.33 at the 68% confidence level. This result is combined with a previous measurement to obtain the most stringent measurement of this quantity by CDF to date, Gf=0.07-0.07+0.15.
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 Supersymmetry inpp¯Collisions ats=1.96 TeVUsing the Trilepton Signature for Chargino-Neutralino Production
We use the three lepton and missing energy trilepton signature to search for chargino-neutralino production with 2.0 fb(-1) of integrated luminosity collected by the CDF II experiment at the Tevatron p (p) over bar collider. We expect an excess of approximately 11 supersymmetric events for a choice of parameters of the mSUGRA model, but our observation of 7 events is consistent with the standard model expectation of 6.4 events. We constrain the mSUGRA model of supersymmetry and rule out chargino masses up to 145 GeV/c(2) for a specific choice of parameters.
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…
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.
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.
Search for a Heavy Toplike Quark inpp¯Collisions ats=1.96 TeV
We present the results of a search for pair production of a heavy toplike (t') quark decaying to Wq final states using data corresponding to an integrated luminosity of 5.6 fb(-1) collected by the CDF II detector in pp collisions at √s=1.96 TeV. We perform parallel searches for t'→Wb and t'→Wq (where q is a generic down-type quark) in events containing a lepton and four or more jets. By performing a fit to the two-dimensional distribution of total transverse energy versus reconstructed t' quark mass, we set upper limits on the t't' production cross section and exclude a standard model fourth-generation t' quark decaying to Wb (Wq) with mass below 358 (340) GeV/c(2) at 95% C.L.
Measurement of theWW+WZProduction Cross Section Using thelepton+jetsFinal State at CDF II
We report two complementary measurements of the diboson (WW + WZ) cross section in the final state consisting of an electron or muon, missing transverse energy, and jets, performed using p{bar p} collision data at {radical}s = 1.96 TeV collected by the Collider Detector at Fermilab. The first method uses the dijet invariant mass distribution while the second method uses more of the kinematic information in the event through matrix-element calculations of the signal and background processes and has a higher sensitivity. The result from the second method has a signal significance of 5.4{sigma} and is the first observation of WW + WZ production using this signature. Combining the results from …
Measurement of Inclusive Jet Cross Sections inZ/γ*(→e+e−)+jetsProduction inpp¯Collisions ats=1.96 TeV
Inclusive jet cross sections in Z/{gamma}* events, with Z/{gamma}* decaying into an electron-positron pair, are measured as a function of jet transverse momentum and jet multiplicity in p{bar p} collisions at {radical}s - 1.96 TeV with the upgraded Collider Detector at Fermilab in Run II, based on an integrated luminosity of 1.7 fb{sup -1}. The measurements cover the rapidity region |y{sup jet}| 30 GeV/c. Next-to-leading order perturbative QCD predictions are in good agreement with the measured cross sections.
Measurements of the top-quark mass using charged particle tracking
21 páginas, 13 figuras, 6 tablas.-- PACS numbers: 12.15.-y, 13.85.-t, 14.60.-z, 14.65.Fy.-- CDF Collaboration: et al.
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), Ï0(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±0.15Ï0(770) per hadronic Z0decay. The average multiplicities of f0(975) for scaled momentum, xp, in the range 0.05â¤xpâ¤0.6 and of f2(1270) for 0.05â¤xpâ¤1.0 are 0.098±0.016 and 0.170±0.043 respectively. The f0(975) and Ï0(770)xp-spectra have similar shapes. The f2(1270)/Ï0(770) ratio increases with xp. The average multiplicities…
First measurement of the ratio of branching fractionsB(Λb0→Λc+μ−ν¯μ)/B(Λb0→Λc+π−)
This article presents the first measurement of the ratio of branching fractions B(Lambda(0)(b) -> Lambda(+)(c) mu(-) (nu) over bar (mu))/B(Lambda(0)(b) -> Lambda(+)(c) pi(-)). Measurements in two control samples using the same technique B((B) over bar (0) -> D+ mu(-) (nu) over bar (mu))/B((B) over bar (0) -> D+ pi(-)) and B((B) over bar (0) -> D*(2010)(+) mu(-) (nu) over bar (mu))/B((B) over bar (0) -> D*(2010)(+) pi(-)) are also reported. The analysis uses data from an integrated luminosity of approximately 172 pb(-1) of p (p) over bar collisions at root s = 1: 96 TeV, collected with the CDF II detector at the Fermilab Tevatron. The relative branching fractions are measured to be B(Lambda(…
Measurement of thett¯production cross section with anin situcalibration ofb-jet identification efficiency
A measurement of the top-quark pair-production cross section in ppbar collisions at sqrt{s}=1.96 TeV using data corresponding to an integrated luminosity of 1.12/fb collected with the Collider Detector at Fermilab is presented. Decays of top-quark pairs into the final states e nu + jets and mu nu + jets are selected, and the cross section and the b-jet identification efficiency are determined using a new measurement technique which requires that the measured cross sections with exactly one and multiple identified b-quarks from the top-quark decays agree. Assuming a top-quark mass of 175 GeV/c^2, a cross section of 8.5+/-0.6(stat.)+/-0.7(syst.) pb is measured.
Search for heavy charged scalars in Z$^0$ Decays
Using a sample of Z0's corresponding to about 12 000 events, we have searched for the production of charged scalars, primarily charged Higgs particles, decaying into c̄scs̄, τν+jets, and τντν. The average detection efficiency is 20%. No candidate was found in the leptonic modes. Masses in the range up to 30-36 GeV/c2 are excluded, extending the mass domain covered by previous e+e- machines.
Strong Evidence forZZProduction inpp¯Collisions ats=1.96 TeV
We report the first measurement of the cross section for Z boson pair production at a hadron collider. This result is based on a data sample corresponding to 1.9 fb{sup -1} of integrated luminosity from p{bar p} collisions at {radical}s = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. In the {ell}{ell}{ell}{prime}{ell}{prime} channel, we observe three ZZ candidates with an expected background of 0.096{sub -0.063}{sup +0.092} events. In the {ell}{ell}{nu}{nu} channel, we use a leading-order calculation of the relative ZZ and WW event probabilities to discriminate between signal and background. In the combination of {ell}{ell}{ell}{prime}{ell}{prime} and {ell}{ell}{nu}{…
Measurement of thepp¯→tt¯production cross section and the top quark mass ats=1.96 TeVin the all-hadronic decay mode
We report the measurements of the t{bar t} production cross section and of the top quark mass using 1.02 fb{sup -1} of p{bar p} data collected with the CDF II detector at the Fermilab Tevatron. We select events with six or more jets on which a number of kinematical requirements are imposed by means of a neural network algorithm. At least one of these jets must be identified as initiated by a b-quark candidate by the reconstruction of a secondary vertex. The cross section is measured to be {sigma}{sub t{bar t}} = 8.3 {+-} 1.0(stat. ){sup +2.0}{sub -1.5}(syst.) {+-} 0.5(lumi.) pb, which is consistent with the standard model prediction. The top quark mass of 174.0 {+-} 2.2(stat.){+-}4.8(syst.)…
Search for a Fermiophobic Higgs Boson Decaying into Diphotons inpp¯Collisions ats=1.96 TeV
A search for a narrow diphoton mass resonance is presented based on data from 3.0 fb{sup -1} of integrated luminosity from p{bar p} collisions at {radical}s = 1.96 TeV collected by the CDF experiment. No evidence of a resonance in the diphoton mass spectrum is observed, and upper limits are set on the cross section times branching fraction of the resonant state as a function of Higgs boson mass. The resulting limits exclude Higgs bosons with masses below 106 GeV/c{sup 2} at a 95% Bayesian credibility level (C.L.) for one fermiophobic benchmark model.
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…
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 > 0.05pbeam (xp > 0.05) and 0.11 ± 0.05 for the f{hook}2 (1270) for xp > 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 the supersymmetric partner of the top quark inpp¯collisions ats=1.96 TeV
We present a search for the lightest supersymmetric partner of the top quark in proton-antiproton collisions at a center-of-mass energy root s = 1: 96 TeV. This search was conducted within the framework of the R parity conserving minimal supersymmetric extension of the standard model, assuming the stop decays dominantly to a lepton, a sneutrino, and a bottom quark. We searched for events with two oppositely-charged leptons, at least one jet, and missing transverse energy in a data sample corresponding to an integrated luminosity of 1 fb(-1) collected by the Collider Detector at Fermilab experiment. No significant evidence of a stop quark signal was found. Exclusion limits at 95% confidence …
Production ofΛ0,Λ¯0,Ξ±, andΩ±hyperons inpp¯collisions ats=1.96 TeV
We report a set of measurements of inclusive invariant ${p}_{T}$ differential cross sections of ${\ensuremath{\Lambda}}^{0}$, ${\overline{\ensuremath{\Lambda}}}^{0}$, ${\ensuremath{\Xi}}^{\ifmmode\pm\else\textpm\fi{}}$, and ${\ensuremath{\Omega}}^{\ifmmode\pm\else\textpm\fi{}}$ hyperons reconstructed in the central region with pseudorapidity $|\ensuremath{\eta}|l1$ and ${p}_{T}$ up to $10\text{ }\text{ }\mathrm{GeV}/c$. Events are collected with a minimum-bias trigger in $p\overline{p}$ collisions at a center-of-mass energy of 1.96 TeV using the CDF II detector at the Tevatron Collider. As ${p}_{T}$ increases, the slopes of the differential cross sections of the three particles are similar,…
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.
Search for Large Extra Dimensions in Final States Containing One Photon or Jet and Large Missing Transverse Energy Produced inpp¯Collisions ats=1.96 TeV
We present the results of searches for large extra dimensions in samples of events with large missing transverse energy E_{T} and either a photon or a jet produced in pp[over ] collisions at sqrt[s]=1.96 TeV collected with the Collider Detector at Fermilab II. For gamma+E_{T} and jet+E_{T} candidate samples corresponding to 2.0 and 1.1 fb;{-1} of integrated luminosity, respectively, we observe good agreement with standard model expectations and obtain a combined lower limit on the fundamental parameter of the large extra dimensions model M_{D} as a function of the number of extra dimensions in the model.
Search for the DecaysB(s)0→e+μ−andB(s)0→e+e−in CDF Run II
We report results from a search for the lepton flavor violating decays $B^0_{(s)}\to e^+\mu^-$, and the flavor-changing neutral-current decays $B^0_{(s)} \to e^+ e^-$. The analysis uses data corresponding to ${\rm 2 fb^{-1}}$ of integrated luminosity of $p \bar{p}$ collisions at $\sqrt{s}=1.96 {\rm TeV}$ collected with the upgraded Collider Detector (CDF II) at the Fermilab Tevatron. The observed number of $B^0_{(s)}$ candidates is consistent with background expectations. The resulting Bayesian upper limits on the branching ratios at 90% credibility level are $\mathcal{B}(B^0_s \to e^{+}\mu^{-}) 47.8 {\rm TeV/c^2}$, and ${M_{LQ}}(B^0\to e^+ \mu^-) > 59.3 {\rm TeV/c^2}$, at 90% credibility l…
Limits on anomalous triple gauge couplings inpp¯collisions ats=1.96 TeV
We present a search for anomalous triple gauge couplings (ATGC) in WW and WZ boson production. The boson pairs are produced in p (p) over bar collisions at root s = 1.96 TeV, and the data sample corresponds to 350 pb(-1) of integrated luminosity collected with the CDF II detector at the Fermilab Tevatron. In this search one W decays to leptons, and the other boson (W or Z) decays hadronically. Combining with a previously published CDF measurement of W gamma boson production yields ATGC limits of -0.18 <lambda < 0.17 and -0.46 <Delta kappa < 0.39 at the 95% confidence level, using a cutoff scale Lambda=1.5 TeV.
Measurement of the top quark mass in the dilepton channel using mT2 at CDF
We present measurements of the top quark mass using mT2, a variable related to the transverse mass in events with two missing particles. We use the template method applied to tt̅ dilepton events produced in pp̅ collisions at Fermilab’s Tevatron Collider and collected by the CDF detector. From a data sample corresponding to an integrated luminosity of 3.4 fb-1, we select 236 tt̅ candidate events. Using the mT2 distribution, we measure the top quark mass to be Mtop=168.0-4.0+4.8(stat)±2.9(syst) GeV/c2. By combining mT2 with the reconstructed top quark mass distributions based on a neutrino weighting method, we measure Mtop=169.3±2.7(stat)±3.2(syst) GeV/c2. This is the first application of …
Search for Maximal Flavor Violating Scalars in Same-Charge Lepton Pairs inpp¯Collisions ats=1.96 TeV
Models of maximal flavor violation (MxFV) in elementary particle physics may contain at least one new scalar SU(2) doublet field {phi}{sub FV}=({eta}{sup 0},{eta}{sup +}) that couples the first and third generation quarks (q{sub 1}, q{sub 3}) via a Lagrangian term L{sub FV}={xi}{sub 13}{phi}{sub FV}q{sub 1}q{sub 3}. These models have a distinctive signature of same-charge top-quark pairs and evade flavor-changing limits from meson mixing measurements. Data corresponding to 2 fb{sup -1} collected by the Collider Dectector at Fermilab II detector in pp collisions at {radical}(s)=1.96 TeV are analyzed for evidence of the MxFV signature. For a neutral scalar {eta}{sup 0} with m{sub {eta}{sup 0}…
Search for the Higgs Boson in Events with Missing Transverse Energy andbQuark Jets Produced inpp¯Collisions ats=1.96 TeV
We search for the standard model Higgs boson produced in association with an electroweak vector boson in events with no identified charged leptons, large imbalance in transverse momentum, and two jets where at least one contains a secondary vertex consistent with the decay of b hadrons. We use {approx}1 fb{sup -1} integrated luminosity of p{bar p} collisions at {radical}s = 1.96 TeV recorded by the CDF II experiment at the Tevatron. We find 268 (16) single (double) b-tagged candidate events, where 248 {+-} 43 (14.4 {+-} 2.7) are expected from standard model background processes. We place 95% confidence level upper limits on the Higgs boson production cross section for several Higgs boson ma…
Search for anomalous production of events with two photons and additional energetic objects at CDF
27 páginas, 17 figuras, 5 tablas.-- CDF Collaboration: et al.
Inclusive Search for Squark and Gluino Production inpp¯Collisions ats=1.96 TeV
We report on a search for inclusive production of squarks and gluinos in p{bar p} collisions at {radical}s = 1.96 TeV, in events with large missing transverse energy and multiple jets of hadrons in the final state. The study uses a CDF Run II data sample corresponding to 2 fb-1 of integrated luminosity. The data are in good agreement with the standard model predictions, giving no evidence for any squark or gluino component. In an R-parity conserving minimal supergravity scenario with A{sub 0} = 0, mu < 0 and tan beta = 5, 95% C.L. upper limits on the production cross sections in the range between 0.1 pb and 1 pb are obtained, depending on the squark and gluino masses considered. For gluino …
Measurements of branching fraction ratios andCPasymmetries inB±→DCPK±decays in hadron collisions
9 paginas, 3 figuras, 2 tablas.-- PACS numbers: 13.25.Hw, 11.30.Er, 14.40.Nd.--CDF Collaboration: et al.
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…
Measurement of theΛb0Lifetime inΛb0→Λc+π−Decays inpp¯Collisions ats=1.96 TeV
We thank the Fermilab staff and the technical staffs of the participating institutions for their vital contributions. This work was supported by the U.S. Department of Energy and National Science Foundation; the Italian Istituto Nazionale di Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and Technology of Japan; the Natural Sciences and Engineering Research Council of Canada; the National Science Council of the Republic of China; the Swiss National Science Foundation; the A.P. Sloan Foundation; the Bundesministerium fur Bildung und Forschung, Germany; the World Class University Program, the National Research Foundation of Korea; the Science and Technology Facilities Co…
Search for the Production of Scalar Bottom Quarks inpp¯Collisions ats=1.96 TeV
We report on a search for direct scalar bottom quark (sbottom) pair production in pp collisions at {radical}(s)=1.96 TeV, in events with large missing transverse energy and two jets of hadrons in the final state, where at least one of the jets is required to be identified as originating from a b quark. The study uses a collider detector at Fermilab Run II data sample corresponding to 2.65 fb{sup -1} of integrated luminosity. The data are in agreement with the standard model. In an R-parity conserving minimal supersymmetric scenario, and assuming that the sbottom decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits on the sbottom pair production cross se…
Search forBs0→μ+μ−andB0→μ+μ−Decays with CDF II
A search has been performed for B{sub s}{sup 0} {yields} {mu}{sup +}{mu}{sup -} and B{sup 0} {yields} {mu}{sup +}{mu}{sup -} decays using 7 fb{sup -1} of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider. The observed number of B{sup 0} candidates is consistent with background-only expectations and yields an upper limit on the branching fraction of {Beta}(B{sup 0} {yields} {mu}{sup +}{mu}{sup -}) < 6.0 x 10{sup -9} at 95% confidence level. We observe an excess of B{sub s}{sup 0} candidates. The probability that the background processes alone could produce such an excess or larger is 0.27%. The probability that the combination of background and the expe…
Search for third generation vector leptoquarks inpp¯collisions ats=1.96 TeV
We search for a third generation vector leptoquark (VLQ3) that decays to a b quark and tau lepton using the CDF II detector and 320pb-1 of integrated luminosity from the Fermilab Tevatron. Observing a number of events in agreement with standard model expectations, we obtain, assuming Yang-Mills (minimal) couplings, the most stringent upper limit on the VLQ3 pair production cross section of 344 fb (493 fb) and lower limit on the VLQ3 mass of 317GeV/c2 (251GeV/c2) at 95% C.L. © 2008 The American Physical Society.
Search for the Production of Narrowtb¯Resonances in1.9 fb−1ofpp¯Collisions ats=1.96 TeV
We present new limits on resonant tb production in ppbar collisions at sqrt(s) = 1.96 TeV, using 1.9 fb{sup -1} of data recorded with the CDF II detector at the Fermilab Tevatron. We reconstruct a putative tb mass in events with a lepton, neutrino candidate, and two or three jets, and search for anomalous tb production as modeled by W{prime} {yields} tb. We set a new limit on a right-handed W{prime} with standard model-like coupling, excluding any mass below 800 GeV at 95% C.L. For any narrow W{prime}-like state with mass above 800 GeV, the cross-section is found to be less than 0.28 pb at 95% C.L. We also present an exclusion of the W{prime} coupling strength versus W{prime} mass.
Measurement ofW-Boson Polarization in Top-Quark Decay inpp¯Collisions ats=1.96 TeV
We report measurements of the polarization of W bosons from top-quark decays using 2.7 fb(-1) of p (p) over bar collisions collected by the CDF II detector. Assuming a top-quark mass of 175 GeV/c(2), three measurements are performed. A simultaneous measurement of the fraction of longitudinal (f(0)) and right-handed (f(0)) W bosons yields the model- independent results f(0) =0. 88 +/- 0.11(stat) +/- 0.06(syst) and f(+) = 0.15 +/- 0.07(stat) +/- 0.06(syst) with a correlation coefficient of -0.59. A measurement of f(0) [f(+)] constraining f(+) [f(0)] to its standard model value of 0.0 [0.7] yields f(0) 0.70 + 0.07(stat) +/- 0.04(syst) [f(+) - 0.01 +/- 0.02(stat) +/- 0.05(syst)]. All these resu…
Inclusive Search for Standard Model Higgs Boson Production in the WW Decay Channel using the CDF II Detector
We present a search for standard model (SM) Higgs boson production using p (p) over bar collision data at root s = 1. 96 TeV, collected with the CDF II detector and corresponding to an integrated luminosity of 4. 8 fb(-1). We search for Higgs bosons produced in all processes with a significant production rate and decaying to two W bosons. We find no evidence for SM Higgs boson production and place upper limits at the 95% confidence level on the SM production cross section (sigma(H)) for values of the Higgs boson mass (m(H)) in the range from 110 to 200 GeV. These limits are the most stringent for m(H) > 130 GeV and are 1.29 above the predicted value of sigma(H) for m(H) 165 GeV.
Search for the neutral current top quark decayt→Zcusing the ratio ofZ-boson+4 jetstoW-boson+4 jetsproduction
We have used the Collider Detector at Fermilab (CDF II) to search for the flavor-changing neutral-current (FCNC) top quark decay t {yields} Zc using a technique employing ratios of W and Z production, measured in p{bar p} data corresponding to an integrated luminosity of 1.52 fb{sup -1}. The analysis uses a comparison of two decay chains, p{bar p} {yields} t{bar t} {yields} WbWb {yields} {ell}{nu}bjjb and p{bar p} {yields} t{bar t} {yields} ZcWb {yields} {ell}{ell}cjjb, to cancel systematic uncertainties in acceptance, efficiency, and luminosity. We validate the modeling of acceptance and efficiency for lepton identification over the multi-year dataset using another ratio of W and Z product…
Observation of theΩb−baryon and measurement of the properties of theΞb−andΩb−baryons
The authors report the observation of the bottom, doubly-strange baryon {Omega}{sub b}{sup -} through the decay chain {Omega}{sub b}{sup -} {yields} J/{psi}{Omega}{sup -}, where J/{psi} {yields} {mu}{sup +} {mu}{sup -}, {Omega}{sup -} {yields} {Lambda}K{sup -}, and {Lambda} {yields} p {pi}{sup -}, using 4.2 fb{sup -1} of data from p{bar p} collisions at {radical}s = 1.96 TeV, and recorded with the Collider Detector at Fermilab. A signal is observed whose probability of arising from a background fluctuation is 4.0 x 10{sup -8}, or 5.5 Gaussian standard deviations. The {Omega}{sub b}{sup -} mass is measured to be 6054.4 {+-} 6.8(stat.) {+-} 0.9(syst.) MeV/c{sup 2}. The lifetime of the {Omega}…
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…
Measurement of thett¯production cross section inpp¯collisions ats=1.96 TeVusing soft electronb-tagging
The authors present a measurement of the t{bar t} production cross section using events with one charged lepton and jets from p{bar p} collisions at a center-of-mass energy of 1.96 TeV. A b-tagging algorithm based on the probability of displaced tracks coming from the event interaction vertex is applied to identify b quarks from top decay. Using 318 pb{sup -1} of data collected with the CDF II detector, they measure the t{bar t} production cross section in events with at least one restrictive (tight) b-tagged jet and obtain 8.9{sub -1.0}{sup +1.0}(stat.){sub -1.0}{sup +1.1}(syst.) pb. The cross section value assumes a top quark mass of m{sub t} is presented in the paper. This result is cons…
Search for Supersymmetry with Gauge-Mediated Breaking in Diphoton Events with Missing Transverse Energy at CDF II
8 páginas, 3 figuras.-- PACS numbers: 12.60.Jv, 13.85.Rm, 13.85.Qk, 14.80.Ly.-- CDF Collaboration: et al.
Search for pair production of neutral Higgs bosons in Z$^0$ decays
The pair production of the lightest scalar Higgs boson, h, and a pseudoscalar Higgs boson, A, was searched for in a data sample containing 10 000 hadronic Z0 decays. The search involved both leptonic and purely hadronic decay channels of each Higgs boson. No signal was found, and limits on the Higgs boson masses, in the framework of the minimal supersymmetric extension of the standard model, ar reported up to 35 GeV/c2 at 95% CL, for both tan β > 1 and tan β < 1, where tan β is the ratio of the vacuum expectation values of the two Higgs doublets.
Measurement of the Ratioσtt¯/σZ/γ*→lland Precise Extraction of thett¯Cross Section
We report a measurement of the ratio of the t (t) over bar to Z/gamma* production cross sections in root s = 1.96 TeV p (p) over bar collisions using data corresponding to an integrated luminosity of up to 4.6 fb(-1), collected by the CDF II detector. The t (t) over bar cross section ratio is measured using two complementary methods, a b-jet tagging measurement and a topological approach. By multiplying the ratios by the well-known theoretical Z/gamma* -> ll cross section predicted by the standard model, the extracted t (t) over bar cross sections are effectively insensitive to the uncertainty on luminosity. A best linear unbiased estimate is used to combine both measurements with the resul…
Adding pseudo-observables to the four-lepton experimentalist’s toolbox
The "golden" channel, in which the newly-discovered Higgs boson decays to four leptons by means of intermediate vector bosons, is important for determining the properties of the Higgs boson and for searching for subtle new physics effects. Different approaches exist for parametrizing the relevant Higgs couplings in this channel; here we relate the use of pseudo-observables to methods based on specifying the most general amplitude or Lagrangian terms for the $HVV$ interactions. We also provide projections for sensitivity in this channel in several novel scenarios, illustrating the use of pseudo-observables, and analyze the role of kinematic distributions and (ratios of) rates in such $H\to4\…
Measurement of the top pair production cross section in the dilepton decay channel inpp¯collisions ats=1.96 TeV
A measurement of the tt production cross section in pp collisions at {radical}(s)=1.96 TeV using events with two leptons, missing transverse energy, and jets is reported. The data were collected with the CDF II detector. The result in a data sample corresponding to an integrated luminosity 2.8 fb{sup -1} is {sigma}{sub tt}=6.27{+-}0.73(stat){+-}0.63(syst){+-}0.39(lum) pb. for an assumed top mass of 175 GeV/c{sup 2}.
Measurement of the cross section forW-boson production in association with jets inpp¯collisions ats=1.96 TeV
We present a measurement of the cross section for W-boson production in association with jets in p{bar p} collisions at {radical}s = 1.96 TeV. The analysis uses a data sample corresponding to an integrated luminosity of 320 pb{sup -1} collected with the CDF II detector. W bosons are identified in their electron decay channel and jets are reconstructed using a cone algorithm. For each W + {ge} n-jet sample (n = 1-4) we measure {sigma}(p{bar p} {yields} W + {ge} n-jet) x {Beta}(W {yields} e{nu}) with respect to the transverse energy E{sub T} of the nth-highest E{sub T} jet above 20 GeV, for a restricted W {yields} e{nu} decay phase space. The cross sections, corrected for all detector effects…
Study of the leptonic decays of the Z0 boson
Measurements are presented of the cross section ratios Rℓ = σℓ(e+e-→ℓ+ℓ -)/σhh(e+e-→hadrons) for ℓ = e, μ and τ using data taken from a scan around the Z0. The results are Re = (5.09±0.32±0.18)%, Rμ = (4.96±0.35±0.17)% and Rτ,=(4.72±0.38± 0.29)% where, for the ratio Re, the t-channel contribution has been subtracted. These results are consistent with the hypothesis of lepton universality and test this hypothesis at the energy scale s ∼ 8300 GeV2. The absolute cross sections σℓ(e+e-→ℓ +ℓ-) have also been measured. From the cross sections the leptonic partial widths Γe = (83.2±3.0±2.4) MeV, (ΓeΓμ) 1/2=(84.6±3.0±2.4) MeV and (ΓeΓτ) 1/2=(82.6±3.3±3.2) MeV have been extracted. Assuming lepton un…
Search for ExclusiveZ-Boson Production and Observation of High-Masspp¯→pγγp¯→pl+l−p¯Events inpp¯Collisions ats=1.96 TeV
We present a search for exclusive Z boson production in proton-antiproton collisions at {radical}s = 1.96 TeV, using the CDF II detector at Fermilab. We observe no exclusive Z {yields} {ell}{sup +}{ell}{sup -} candidates and place the first upper limit on the exclusive Z cross section in hadron collisions, {sigma}{sub excl}(Z) 40 GeV=c{sup 2} and |{eta}{sub {ell}}| < 4 to be {sigma} = 0.24{sub -0.10}{sup +0.13} pb, which is the first measurement for this mass range and is consistent with the standard model prediction.
Search for New Physics with a Dijet Plus MissingETSignature inpp¯Collisions ats=1.96 TeV
We present results of a signature-based search for new physics using a dijet plus missing transverse energy (E{sub T}) data sample collected in 2 fb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV with the CDF II detector at the Fermilab Tevatron. We observe no significant event excess with respect to the standard model prediction and extract a 95% C.L. upper limit on the cross section times acceptance for a potential contribution from a non-standard model process. Based on this limit the mass of a potential first or second generation scalar leptoquark is constrained to be above 187 GeV/c{sup 2}.
Observation of the rare B(s)(0) + decay from the combined analysis of CMS and LHCb data.
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported licence.-- et al.
Measurement ofb-jet shapes in inclusive jet production inpp¯collisions ats=1.96 TeV
We present a measurement of the shapes of b-jets using 300 pb(-1) of data obtained with the upgraded Collider Detector at Fermilab (CDF II) in p(p)overbar collisions at center-of-mass energy root s=1.96 TeV. This measurement covers a wide transverse momentum range, from 52 to 300 GeV/c. Samples of heavy-flavor enhanced jets together with inclusive jets are used to extract the average shapes of b-jets. The b-jets are expected to be broader than inclusive jets. Moreover, b-jets containing a single b-quark are expected to be narrower than those containing a b(b)overbar pair from gluon splitting. The measured b-jet shapes are found to be significantly broader than expected from the PYTHIA and H…
Top quark mass measurement in thett¯all hadronic channel using a matrix element technique inpp¯collisions ats=1.96 TeV
We present a measurement of the top quark mass in the all hadronic channel ($t\overline{t}\ensuremath{\rightarrow}b\overline{b}{q}_{1}{\overline{q}}_{2}{q}_{3}{\overline{q}}_{4}$) using $943\text{ }\text{ }{\mathrm{pb}}^{\ensuremath{-}1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\text{ }\text{ }\mathrm{TeV}$ collected at the CDF II detector at Fermilab (CDF). We apply the standard model production and decay matrix element (ME) to $t\overline{t}$ candidate events. We calculate per-event probability densities according to the ME calculation and construct template models of signal and background. The scale of the jet energy is calibrated using additional templates formed with the invaria…
Search for New Bottomlike Quark Pair DecaysQQ¯→(tW∓)(t¯W±)in Same-Charge Dilepton Events
We report the most restrictive direct limits on masses of fourth-generation down-type quarks b{sup '}, and quarklike composite fermions (B or T{sub 5/3}), decaying promptly to tW{sup +}-. We search for a significant excess of events with two same-charge leptons (e, mu), several hadronic jets, and missing transverse energy. An analysis of data from pp collisions with an integrated luminosity of 2.7 fb{sup -1} collected with the CDF II detector at Fermilab yields no evidence for such a signal, setting mass limits m{sub b}{sup '}, m{sub B}>338 GeV/c{sup 2} and m{sub T{sub 5{sub /{sub 3}}}}>365 GeV/c{sup 2} at 95% confidence level.
Searching the inclusiveℓγE̸T+b-quark signature for radiative top quark decay and non-standard-model processes
We compare the inclusive production of events containing a lepton (l), a photon ({gamma}), significant transverse momentum imbalance (Ee{sub T}), and a jet identified as containing a b-quark, to SM predictions. The search uses data produced in proton-antiproton collisions at {radical}(s)=1.96 TeV corresponding to 1.9 fb{sup -1} of integrated luminosity taken with the CDF detector. We find 28 l{gamma}bEe{sub T} events versus an expectation of 31.0{sub -3.5}{sup +4.1} events. If we further require events to contain at least three jets and large total transverse energy, the largest SM source is radiative top-quark pair production, tt+{gamma}. In the data we observe 16 tt{gamma} candidate event…
Search for chargino-neutralino production inpp¯collisions ats=1.96 TeVwith high-pTleptons
We present a search for the associated production of charginos and neutralinos in pp collisions at s=1.96TeV. The data were collected at the Collider Detector at Fermilab (CDF II) and correspond to integrated luminosities between 0.7 and 1.0fb-1. We look for final states with one high-pT electron or muon, and two additional leptons. Our results are consistent with the standard model expectations, and we set limits on the cross section as a function of the chargino mass in three different supersymmetric scenarios. For a specific minimal supersymmetric standard model scenario with no slepton mixing, we set a 95% C.L. limit at 151GeV/c2. © 2008 The American Physical Society.
Measurement ofZγproduction inpp¯collisions ats=1.96 TeV
The production rate and kinematics of photons produced in association with Z bosons are studied using 2 fb{sup -1} of p{bar p} collision data collected at the Collider Detector at Fermilab. The cross section for p{bar p} {yields} {ell}{sup +}{ell}{sup -}{gamma} + X (where the leptons {ell} are either muons or electrons with dilepton mass M{sub {ell}{ell}} > 40 GeV/c{sup 2}, and where the photon has transverse energy E{sub T}{sup {gamma}} > 7 GeV and is well separated from the leptons) is 4.6 {+-} 0.2 (stat) {+-} 0.3 (syst) {+-} 0.3 (lum) pb, which is consistent with standard model expectations. We use the photon ET distribution from Z{gamma} events where the Z has decayed to {mu}{sup +}{mu}…
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.
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…
Observation of the Baryonic Flavor-Changing Neutral Current Decay Λb0→Λμ+μ-
8 páginas, 2 figuras, 4 tablas.-- PACS numbers: 13.30.Ce, 12.15.Mm, 14.20.Mr.-- CDF Collaboration: et al.
Search for new particles leading toZ+jetsfinal states inpp¯collisions ats=1.96 TeV
We present the results of a search for new particles that lead to a Z boson plus jets in p{bar p} collisions at {radical}s = 1.96 TeV using the Collider Detector at Fermilab (CDF II). A data sample with a luminosity of 1.06 fb{sup -1} collected using Z boson decays to ee and {mu}{mu} is used. We describe a completely data-based method to predict the dominant background from standard-model Z+jet events. This method can be similarly applied to other analyses requiring background predictions in multi-jet environments, as shown when validating the method by predicting the background from W+jets in t{bar t} production. No significant excess above the background prediction is observed, and a limi…
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.
Search for the Higgs Boson Produced in Association withZ→ℓ+ℓ−inpp¯Collisions ats=1.96 TeV
We present a search for associated production of the standard model (SM) Higgs boson and a Z boson where the Z boson decays to two leptons and the Higgs decays to a pair of b quarks in p{bar p} collisions at the Fermilab Tevatron. We use event probabilities based on SM matrix elements to construct a likelihood function of the Higgs content of the data sample. In a CDF data sample corresponding to an integrated luminosity of 2.7 fb{sup -1} we see no evidence of a Higgs boson with a mass between 100 GeV/c{sup 2} and 150 GeV/c{sup 2}. We set 95% confidence level (C.L.) upper limits on the cross-section for ZH production as a function of the Higgs boson mass m{sub H}; the limit is 8.2 times the…
Measurement ofbHadron Lifetimes in Exclusive Decays Containing aJ/ψinpp¯Collisions ats=1.96 TeV
We report on a measurement of b-hadron lifetimes in the fully reconstructed decay modes B{sup +}{yields}J/{psi}K{sup +}, B{sup 0}{yields}J/{psi}K{sup *}(892){sup 0}, B{sup 0}{yields}J/{psi}K{sub s}{sup 0}, and {Lambda}{sub b}{sup 0}{yields}J/{psi}{Lambda}{sup 0} using data corresponding to an integrated luminosity of 4.3 fb{sup -1}, collected by the CDF II detector at the Fermilab Tevatron. The measured lifetimes are {tau}(B{sup +})=[1.639{+-}0.009(stat){+-}0.009(syst)] ps, {tau}(B{sup 0})=[1.507{+-}0.010(stat){+-}0.008(syst)] ps, and {tau}({Lambda}{sub b}{sup 0})=[1.537{+-}0.045(stat){+-}0.014(syst)] ps. The lifetime ratios are {tau}(B{sup +})/{tau}(B{sup 0})=[1.088{+-}0.009(stat){+-}0.004…
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…
Search for Gluino-Mediated Bottom Squark Production inpp¯Collisions ats=1.96 TeV
We report on a search for the supersymmetric partner of the bottom quark produced from gluino decays in data from 2.5 fb{sup -1} of integrated luminosity collected by the Collider Detector at Fermilab at {radical}s = 1.96 TeV. Candidate events are selected requiring two or more jets and large missing transverse energy. At least two of the jets are required to be tagged as originating from a b quark to enhance the sensitivity. The results are in good agreement with the prediction of the standard model processes, giving no evidence for gluino decay to sbottom quarks. This result constrains the gluino-pair-production cross section to be less than 40 fb at 95% credibility level for a gluino mas…
First simultaneous measurement of the top quark mass in thelepton+jetsand dilepton channels at CDF
We present a measurement of the mass of the top quark using data corresponding to an integrated luminosity of 1.9 fb{sup -1} of pp collisions collected at {radical}(s)=1.96 TeV with the CDF II detector at Fermilab's Tevatron. This is the first measurement of the top quark mass using top-antitop pair candidate events in the lepton+jets and dilepton decay channels simultaneously. We reconstruct two observables in each channel and use a nonparametric kernel density estimation technique to derive two-dimensional probability density functions from simulated signal and background samples. The observables are the top quark mass and the invariant mass of two jets from the W decay in the lepton+jets…
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.