0000000000907175
AUTHOR
A. Wenger
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 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.
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 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 ...
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…
Observation and Properties of the Orbitally ExcitedBs2*Meson
We report the direct observation of the excited L=1 state B_{s2}* in fully reconstructed decays to B+K-. The mass of the B_{s2}* meson is measured to be {5839.6 +- 1.1 (stat.) +- 0.7 (syst.) MeV/c^2, and its production rate relative to the B+ meson is measured to be [1.15 +- 0.23 (stat.) +- 0.13 (syst.)] %.
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 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 +…
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 of the differential cross section for the production of an isolated photon with associated jet in pp¯ collisions at s=1.96 TeV
The process ppbar -> photon + jet + X is studied using 1.0 fb^-1 of data collected by the D0 detector at the Fermilab Tevatron ppbar collider at a center-of-mass energy sqrt(s)=1.96 TeV. Photons are reconstructed in the central rapidity region |y_gamma|<1.0 with transverse momenta in the range 3015 GeV. The differential cross section d^3sigma/dPt_gamma dy_gamma dy_jet is measured as a function of Pt_gamma in four regions, differing by the relative orientations of the photon and the jet in rapidity. Ratios between the differential cross sections in each region are also presented. Next-to-leading order QCD predictions using different parameterizations of parton distribution functions and theo…
Search for scalar top quarks in the acoplanar charm jets and missing transverse energy final state in pp¯ collisions at s=1.96 TeV
We present a search for the pair production of scalar top quarks, $\tilde{t}$, using 995 pb$^{-1}$ of data collected in $p\bar{p}$ collisions with the D0 detector at the Fermilab Tevatron Collider at $\sqrt{s} = 1.96$ TeV. Both scalar top quarks are assumed to decay into a charm quark and a neutralino ($\tilde{\chi}^{0}_{1}$), where $\tilde{\chi}^{0}_{1}$ is the lightest supersymmetric particle. This leads to a final state with two acoplanar charm jets and missing transverse energy. We find the yield of such events to be consistent with the standard model expectation, and exclude sets of $\tilde{t}$ and $\tilde{\chi}^{0}_{1} $ masses at the 95% C.L. that substantially extend the domain excl…
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.
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 …
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 …
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 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 …
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.
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.
Search for the lightest scalar top quark in events with two leptons in pp¯ collisions at s=1.96 TeV
Abstract We report results of a search for the pair production of the lightest supersymmetric partner of the top quark, t ˜ 1 , using a data set corresponding to an integrated luminosity of 1 fb −1 collected by the DO detector at a p p ¯ center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. Both scalar top quarks are assumed to decay into a b quark, a charged lepton and a scalar neutrino. The search is performed in the electron plus muon and dielectron final states. The signal topology consists of two isolated leptons, missing transverse energy, and jets. We find no evidence for this process and exclude regions of parameter space in the framework of the minimal supersymmetric…
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 pair production of second generation scalar leptoquarks
We report on a search for the pair production of second generation scalar leptoquarks (LQ) in ppbar collisions at the center of mass energy sqrt(s)=1.96 TeV using a data set corresponding to an integrated luminosity of 1.0 fb-1 collected with the D0 experiment at the Fermilab Tevatron Collider. Topologies arising from the LQLQbar->muqnuq and LQLQbar->muqmuq decay modes are investigated. No excess of data over the standard model prediction is observed and upper limits on the leptoquark pair production cross section are derived at the 95% C.L. as a function of the leptoquark mass and the branching fraction beta for the decay LQ->muq. These are interpreted as lower limits on the lepto…
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…
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…
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, …
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 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 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…
Erratum to: “Measurement of the isolated photon cross section in pp¯ collisions at s=1.96 TeV” [Phys. Lett. B 639 (2006) 151]
Measurement of the isolated photon cross section in p(p)over-bar collisions at root s = 1.96 TeV (vol 639, pg 151, 2006)
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 a Higgs boson produced in association with a Z boson
We describe a search for the Standard Model Higgs boson with a mass of 105 GeV/c(2) to 145 GeV/c(2) in data corresponding to an integrated luminosity of approximately 450 pb(-1) collected with the D phi detector at the Fermilab Tevatron p (p) over bar collider at a center-of-mass energy of 1.96 TeV. The Higgs boson is required to be produced in association with a Z boson, and the Z boson is required to decay to either electrons or muons with the Higgs boson decaying to a b (b) over bar pair. The data are well described by the expected background, leading to 95% confidence level cross section upper limits sigma (p (p) over bar -> ZH) x B(H -> b (b) over bar) in the range of 3.1 pb to 4.4 pb.
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.
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.
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 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.
Zγ production and limits on anomalous ZZγ and Zγγ couplings in pp¯ collisions at s=1.96 TeV
We present a study of eey and mu mu gamma events using 1109 (1009) pb-(1) of data in the electron (muon) channel, respectively. These data were collected with the DO detector at the Fermilab Tevatron pp collider at Is = 1.96 TeV. Having observed 453 (515) candidates in the eey (jtAy) final state, we measure the Z gamma production cross section for a photon with transverse energy ET > 7 GeV, separation between the photon and leptons Delta Rey > 0.7, and invariant mass of the di-lepton pair Mee > 30 GeV/(2)(c), to be 4.96 0.30(stat. + syst.) zE 0.30(lumi.) pb, in agreement with the Standard Model prediction of 4.74 0.22 pb. This is the most precise Zy cross section measurement at a hadron col…
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…
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…
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-) < 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 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 $80 < m_{H^{\pm} < 155$ 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 $B(t \to H^+b) > 0.24$ for $m_{H^{\pm}=80$ GeV, and $B(t \to H^+b) > 0.19$ for $m_{H^{\pm}=155$ GeV, at the 95% C.L.
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. …
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…
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.
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.).
Measurement of the ratio of the pp¯→W+c-jet cross section to the inclusive pp¯→W+jets cross section
We present a measurement of the fraction of inclusive W +jets events produced with net charm quantum number 11, denoted W + c-jet, in p collisions at root s = 1.96 TeV using approximately 1 fb(-1) of data collected by the DO detector at the Fermilab Tevatron Collider. We identify the W +jets events via the leptonic W boson decays. Candidate W + c-jet events are selected by requiring a jet containing a muon in association with a reconstructed W boson and exploiting the charge correlation between this muon and W boson decay lepton to perform a nearly model-independent background subtraction. We measure the fraction of W + c-jet events in the inclusive W +jets sample for jet PT > 20 GeV and ps…
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.
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 supersymmetry in di-photon final states at s=1.96 TeV
We report results of a search for supersymmetry (SUSY) with gauge-mediated symmetry breaking in di-photon events collected by the DO experiment at the Fermilab Tevatron Collider in 2002-2006. In 1.1 fb(-1) of data, we find no significant excess beyond the background expected from the standard model and set the most stringent lower limits to date for a standard benchmark model on the lightest neutralino and chargino masses of 125 GeV and 229 GeV, respectively, at 95% confidence.
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.
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…
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 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->lnu events produced at hadron colliders. The recoil is chosen from a library of recoils in Z->ll data events and overlaid on a simulated W->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…
A combined search for the standard model Higgs boson at s=1.96 TeV
AbstractWe present new results of the search for WH→ℓνbb¯ production in pp¯ collisions at a center-of-mass energy of s=1.96 TeV, based on a dataset with integrated luminosity of 0.44 fb−1. We combine these new results with previously published searches by the D0 collaboration, for WH and ZH production analyzed in the E̸Tbb¯ final state, for ZH (→ℓ+ℓ−bb¯) production, for WH (→WWW) production, and for H (→WW) direct production. No signal-like excess is observed either in the WH analysis or in the combination of all D0 Higgs boson analyses. We set 95% C.L. (expected) upper limits on σ(pp¯→WH)×B(H→bb¯) ranging from 1.6 (2.2) pb to 1.9 (3.3) pb for Higgs boson masses between 105 and 145 GeV, to …
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.
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.
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.
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.
Search for tt¯ resonances in the lepton plus jets final state in pp¯ collisions at s=1.96TeV
We present a search for a narrow-width heavy resonance decaying into top quark pairs X->ttbar in ppbar collisions at sqrt{s}=1.96TeV using approximately 0.9fb^-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. This analysis considers ttbar candidate events in the lepton plus jets channel with at least one identified b jet and uses the ttbar invariant mass distribution to search for evidence of resonant production. We find no evidence for a narrow resonance X decaying to ttbar. Therefore, we set upper limits on sigma*B(X->ttbar) for different hypothesized resonance masses using a Bayesian approach. For a Topcolor-assisted technicolor model, the existence of a leptop…
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…
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.
Search for a scalar or vector particle decaying into Zγ in pp¯ collisions at s=1.96 TeV
We present a search for a narrow scalar or vector resonance decaying into Z gamma with a subsequent Z boson decay into a pair of electrons or moons. The data for this search were collected with the D circle divide detecror at the Fermilab Tevatron p (p) over bar collider at a center of mass energy root s = 1.96 TeV. Using 1.1 (1.0) fb(-1) of data, we observe 49 (50) candidate events in the electron (muon) channel, in good agreement with the standard model prediction. From the combination of both channels, we derive 95% C.L. upper limits on the cross section times branching fraction (sigma x B) into Z gamma. These limits range from 0.19 (0.20) pb for a scalar (vector) resonance mass of 600 G…
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 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.
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 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 -> 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 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.
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.
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.