arXiv subjects

V. Abazov

Publications and source records attributed to V. Abazov.

At least 73 records · Page 4Linked to original sources

arXiv2009

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.

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arXiv2009

Search for squark production in events with jets, hadronically decaying tau leptons and missing transverse energy at sqrt(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 ppbar collision data from the Fermilab Tevatron Collider at a center of mass energy of 1.96 TeV recorded by the D0 detector is analyzed. Results are combined with the previously published D0 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 tau leptons dominate. Gaugino masses m_1/2 are excluded up to 172 GeV.

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arXiv2009

Search for the lightest scalar top quark in events with two leptons in ppbar collisions at sqrt(s)=1.96 TeV

We report results of a search for the pair production of the lightest supersymmetric partner of the top quark using 1 fb-1 of data collected by the D0 detector at a ppbar 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 standard model.

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arXiv2009

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

We search for charged massive long-lived particles using 1.1 fb$^{-1}$ of data collected by the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider. Time-of-flight information is used to search for pair produced long-lived tau sleptons, gaugino-like 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 0.31pb to 0.04pb for stau masses between 60 GeV and 300 GeV. We also set lower mass limits of 206 GeV (171 GeV) for pair produced charged gauginos (higgsinos).

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arXiv2009

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 analyze 83 candidate events in data and obtain m_t = 176.2 +/- 4.8 (stat) +/- 2.1 (sys) GeV and m_t = 173.2 +/- 4.9 (stat) +/- 2.0 (sys) GeV for the two methods, respectively. Accounting for correlations between the two methods, we combine the measurements to obtain m_t = 174.7 +/- 4.4 (stat) +/- 2.0 (sys) GeV.

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arXiv2009

Measurement of the B0_s semileptonic branching ratio to an orbitally excited D_s** state, Br(B0_s -> Ds1(2536) mu nu)

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.

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arXiv2009

Search for admixture of scalar top quarks in the ttbar lepton+jets final state at sqrt(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.

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arXiv2009

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.

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arXiv2008

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.

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arXiv2008

Observation of the doubly strange b baryon Omega_b-

We report the observation of the doubly strange b baryon Omega_b- in the decay channel Omega_b- to J/psi Omega-, with J/psi to mu+ mu- and Omega- to Lambda K-, in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ 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.

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arXiv2008

Measurement of differential Z/gamma*+jet+X cross sections in proton anti-proton collisions at sqrt{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 generator are also compared to the measurements. These show significant overall normalization differences to the data and have varied success in describing the shape of the distributions.

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arXiv2008

Search for neutral Higgs bosons at high tan(beta) in the b(h/H/A)->btautau channel

The first search in ppbar collisions at sqrt(s)=1.96 GeV 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 (SM), 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.

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arXiv2008

Observation of ZZ production in ppbar collisions at sqrt(s) = 1.96 TeV

We present an observation for ZZ -> l+l-l'+l'- (l, l' = e or mu) production in ppbar collisions at a center-of-mass energy of sqrt(s) = 1.96 TeV. Using 1.7 fb-1 of data collected by the D0 experiment at the Fermilab Tevatron Collider, we observe three candidate events with an expected background of 0.14 +0.03 -0.02 events. The significance of this observation is 5.3 standard deviations. The combination of D0 results in this channel, as well as in ZZ -> l+l-nunubar, yields a significance of 5.7 standard deviations and a combined cross section of sigma(ZZ) = 1.60 +/- 0.63 (stat.) +0.16 -0.17 (syst.) pb.

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arXiv2008

Measurement of the shape of the boson transverse momentum distribution in ppbar -> Z/gamma* -> ee+X events produced at sqrt{s}=1.96 TeV

We present a measurement of the shape of the Z/gamma* boson transverse momentum (qT) distribution in ppbar -> Z/gamma* -> ee+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 qT, but above the perturbative QCD calculation in the region of qT>30 GeV/c. Using events with qT<30 GeV/c, we extract the value of g2, one of the non-perturbative 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 resummed form factor with modifications in the small Bjorken x region of the proton wave function.

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arXiv2008

ZZ to llvv production in pp collisions at sqrt(s) = 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.

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arXiv2008

Measurement of the angular and lifetime parameters of the decays $B_{d}^{0}\to J/ψK^{*0}$ and $B_{s}^{0}\to J/ψϕ$

We present measurements of the linear polarization amplitudes and the strong relative phases that describe the flavor-untagged decays $B_{d}^{0}\to J/ψK^{*0}$ and $B_{s}^{0}\to J/ψϕ$ in the transversity basis. We also measure the mean lifetime $\barτ_{s}$ of the $B_{s}^{0}$ mass eigenstates and the lifetime ratio $\barτ_{s}/τ_{d}$. 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 $B_{d}^{0}\to J/ψK^{*0}$ decay.

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arXiv2008

Search for scalar leptoquarks and T-odd quarks in the acoplanar jet topology using 2.5 fb-1 of ppbar collision data at sqrt(s)=1.96 TeV

A search for new physics in the acoplanar jet topology has been performed in 2.5 fb-1 of data from ppbar collisions at sqrt(s)=1.96 TeV, recorded by the D0 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 mass.

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arXiv2008

Precise measurement of the top quark mass from lepton+jets events at D0

We measure the mass of the top quark using top quark pair candidate events in the lepton+jets channel from data corresponding to 1 fb-1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron collider. We use a likelihood technique that reduces the jet energy scale uncertainty by combining an in-situ jet energy calibration with the independent constraint on the jet energy scale (JES) from the calibration derived using photon+jets and dijet samples. We find the mass of the top quark to be 171.5+-1.8(stat.+JES)+-1.1(syst.) GeV.

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