arXiv subjects

V. M. Abazov

Publications and source records attributed to V. M. Abazov.

At least 73 records · Page 4Linked to original sources

arXiv2006

Measurement of Bd mixing using opposite-side flavor tagging

We report on a measurement of the $B^0_d$ mixing frequency and the calibration of an opposite-side flavor tagger in the DØexperiment. Various properties associated with the $b$ quark on the opposite side of the reconstructed $B$ meson were combined using a likelihood-ratio method into a single variable with enhanced tagging power. Its performance was tested with data, using a large sample of reconstructed semileptonic $B \to μ\dzero X$ and $B \to μ\dst X$ decays, corresponding to an integrated luminosity of approximately 1 fb$^{-1}$. The events were divided into groups depending on the value of the combined tagging variable, and an independent analysis was performed in each group. Combining the results of these analyses, the overall effective tagging power was found to be eD^2 = (2.48 \pm 0.21 (stat.) ^{+0.08}_{-0.06} (syst.))%. The measured $B^0_d$ mixing frequency dmd = 0.506 \pm 0.020 {\rm (stat) \pm 0.016 (syst) ps}^{-1} is in good agreement with the world average value.

hep-ex↗

arXiv2006

Search for scalar leptoquarks in the acoplanar jet topology in ppbar collisions at sqrt(s)=1.96 TeV

A search for leptoquarks has been performed in 310 pb-1 of data from ppbar collisions at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron Collider. The topology analyzed consists of acoplanar jets with missing transverse energy. The data show good agreement with standard model expectations, and a lower mass limit of 136 GeV has been set at the 95% C.L. for a scalar leptoquark decaying exclusively into a quark and a neutrino.

hep-ex↗

arXiv2006

Search for a heavy resonance decaying into a Z+jet final state in p-pbar collisions at sqrt(s) = 1.96 TeV using the D0 detector

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

hep-ex↗

arXiv2006

Search for R-parity violating supersymmetry via the LLE couplings lambda_{121}, lambda_{122} or lambda_{133} in ppbar collisions at sqrt(s)=1.96 TeV

A search for gaugino pair production with a trilepton signature in the framework of R-parity violating supersymmetry via the couplings lambda_121, lambda_122, or lambda_133 is presented. The data, corresponding to an integrated luminosity of L~360/pb, were collected from April 2002 to August 2004 with the D0 detector at the Fermilab Tevatron Collider, at a center-of-mass energy of sqrt(s)=1.96 TeV. This analysis considers final states with three charged leptons with the flavor combinations eel, mumul, and eetau (l=e or mu). No evidence for supersymmetry is found and limits at the 95% confidence level are set on the gaugino pair production cross section and lower bounds on the masses of the lightest neutralino and chargino are derived in two supersymmetric models.

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arXiv2005

Search for Randall-Sundrum Gravitons in Dilepton and Diphoton Final States

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

hep-ex↗

arXiv2005

Measurement of the Lifetime Difference in the B_s^0 System

We present a study of the decay B_s^0 -> J/psi phi We obtain the CP-odd fraction in the final state at time zero, R_perp = 0.16 +/- 0.10 (stat) +/- 0.02 (syst), the average lifetime of the (B_s, B_sbar) system, tau (B_s^0) =1.39^{+0.13}_{-0.16} (stat) ^{+0.01}_{-0.02} (syst) ps, and the relative width difference between the heavy and light mass eigenstates, Delta Gamma/Gamma = (Gamma_L - Gamma_H)/Gamma =0.24^{+0.28}_{-0.38} (stat) ^{+0.03}_{-0.04} (syst). With the additional constraint from the world average of the B_s^0$lifetime measurements using semileptonic decays, we find tau (B_s^0)= 1.39 +/- 0.06 ~ps and Delta Gamma/Γ= 0.25^{+0.14}_{-0.15}. For the ratio of the B_s^0 and B^0 lifetimes we obtain tau(B_s^0)/tau(B^0)} = 0.91 +/- 0.09 (stat) +/- 0.003 (syst).

hep-ex↗

arXiv2005

Measurement of $\bm{σ(p \bar p \to Z) \cdot}$Br$\bm{(Z \to ττ)}$ at $\bm{\sqrt{s}=}$1.96 TeV

We present a measurement of the cross section for $Z$ production times the branching fraction to $τ$ leptons, $σ\cdot$Br$(Z\to τ^+ τ^-)$, in $p \bar p$ collisions at $\sqrt{s}=$1.96 TeV in the channel in which one $τ$ decays into $μν_μ ν_τ$, and the other into $\rm {hadrons} + ν_τ$ or $e ν_e ν_τ$. The data sample corresponds to an integrated luminosity of 226 pb$^{-1}$ collected with the DØdetector at the Fermilab Tevatron collider. The final sample contains 2008 candidate events with an estimated background of 55%. From this we obtain $σ\cdot$Br$(Z \to τ^+ τ^-)=237 \pm 15$(stat)$\pm 18$(sys)$ \pm 15$(lum) pb, in agreement with the standard model prediction.

hep-ex↗

arXiv2005

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s} = 1.96 TeV using Kinematic Characteristics of Lepton + Jets Events

We present a measurement of the top quark pair ttbar production cross section in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb**{-1} of data collected by the DO detector at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), large missing transverse energy, and at least four jets, and extract the ttbar content of the sample based on the kinematic characteristics of the events. For a top quark mass of 175 GeV, we measure sigma(ttbar) = 6.7 {+1.4-1.3} (stat) {+1.6- 1.1} (syst) +/-0.4 (lumi) pb, in good agreement with the standard model prediction.

hep-ex↗

arXiv2005

Production of WZ Events in p-barp Collisions at sqrt(s)=1.96 TeV and Limits on Anomalous WWZ Couplings

We present results from a search for WZ production with subsequent decay to l nu l'-bar l' (l and l'=electron or muon) using 0.30 fb^(-1) of data collected by the DO experiment between 2002 and 2004 at the Tevatron. Three events with WZ decay characteristics are observed. With an estimated background of 0.71+-0.08 events, we measure the WZ production cross section to be 4.5 (+3.8 -2.6) pb, with a 95% C.L. upper limit of 13.3 pb. The 95% C.L. limits for anomalous WWZ couplings are found to be -2.0 < Delta kappa_Z < 2.4 for form factor scale Lambda = 1 TeV, and -0.48 < lambda_Z < 0.48 and -0.49 < Delta g_1^Z < 0.66 for Lambda = 1.5 TeV.

hep-ex↗

arXiv2005

Measurement of the p-pbar -> Wgamma + X cross section at sqrt(s) = 1.96 TeV and WWgamma anomalous coupling limits

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

hep-ex↗

arXiv2005

The Muon System of the Run II D0 Detector

We describe the design, construction and performance of the upgraded DO muon system for Run II of the Fermilab Tevatron collider. Significant improvements have been made to the major subsystems of the DO muon detector: trigger scintillation counters, tracking detectors, and electronics. The Run II central muon detector has a new scintillation counter system inside the iron toroid and an improved scintillation counter system outside the iron toroid. In the forward region, new scintillation counter and tracking systems have been installed. Extensive shielding has been added in the forward region. A large fraction of the muon system electronics is also new.

physics.ins-det↗

arXiv2005

Study of $Zγ$ events and limits on anomalous $ZZγ$ and $Zγγ$ couplings in ppbar collisions at $sqrt(s) = 1.96$ TeV

We present a measurement of the Zγproduction cross section and limits on anomalous ZZγand Zγγcouplings for form-factor scales of Lambda = 750 and 1000 GeV. The measurement is based on 138 (152) candidate events in the eeγ(μμγ) final state using 320 (290) pb^{-1} of ppbar collisions at \sqrt{s} = 1.96 TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are |h_{10,30}^{Z}|<0.23, |h_{20,40}^{Z}|<0.020, |h_{10,30}^γ|<0.23, and |h_{20,40}^γ|<0.019 for Lambda = 1000 GeV.

hep-ex↗

arXiv2005

Measurement of inclusive differential cross sections for Upsilon(1S) production in p-pbar collisions at sqrt(s) = 1.96 TeV

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

hep-ex↗

arXiv2004

A Search for the Flavor-Changing Neutral Current Decay B0_s -> mu^+mu^- in pp(bar) Collisions at \sqrt{s} = 1.96 TeV with the D0 Detector

We present the results of a search for the flavor-changing neutral current decay B0_s -> mu+ mu- using a data set with integrated luminosity of 240 pb^{-1} of pp(bar) collisions at sqrt{s}=1.96 TeV collected with the D0 detector in Run II of the Fermilab Tevatron collider. We find the upper limit on the branching fraction to be Br(B0_s -> mu+ mu-) \leq 5.0 x 10^{-7} at the 95% C.L. assuming no contributions from the decay B0_d -> mu+ mu- in the signal region. This limit is the most stringent upper bound on the branching fraction B0_s -> mu+ mu- to date.

hep-ex↗

arXiv2004

Measurement of the B^0_s lifetime in the exclusive decay channel B^0_s -> J/psi phi

Using the exclusive decay B^0_s -> J/psi (mu+mu-) phi(K+K-), we report the most precise single measurement of the B^0_s lifetime. The data sample corresponds to an integrated luminosity of approximately 220 pb-1 collected with the DO detector at the Fermilab Tevatron Collider in 2002-2004. We reconstruct 337 signal candidates, from which we extract the B^0_s lifetime, τ(B^0_s) = 1.444 +0.098/-0.090 stat +/- 0.020 sys ps. We also report a measurement for the lifetime of the B^0 meson using the exclusive decay B^0 -> J/psi (mu+mu-)K*0(892)(K+pi-). We reconstruct 1370 signal candidates, obtaining τ(B^0) = 1.473 +0.052/-0.050 stat +/- 0.023 sys ps, and the ratio of lifetimes, τ(B^0_s)/τ(B^0) = 0.980 +0.076/-0.071 stat +/- 0.003 sys.

hep-ex↗

arXiv2004

Search for first-generation scalar leptoquarks in ppbar collisions at sqrt(s)=1.96 TeV

We report on a search for pair production of first-generation scalar leptoquarks (LQ) in ppbar collisions at sqrt(s)=1.96 TeV using an integrated luminosity of 252pb-1 collected at the Fermilab Tevatron collider by the D0 detector. We observe no evidence for LQ production in the topologies arising from LQLQbar->eqeq and LQLQbar->eqnuq, and derive 95% C.L. lower limits on the LQ mass as a function of beta, where beta is the branching fraction for LQ->eq. The limits are 241 and 218 GeV/c2 for beta=1 and 0.5, respectively. These results are combined with those obtained by D0 at sqrt(s)=1.8 TeV, which increases these LQ mass limits to 256 and 234 GeV/c2.

hep-ex↗

arXiv2004

A Search for Anomalous Heavy-Flavor Quark Production in Association with W Bosons

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

hep-ex↗

arXiv2004

Measurement of the Top Quark Mass In All-Jet Events

We describe a measurement of the mass of the top quark from the purely hadronic decay modes of t-tbar pairs using all-jet data produced in p-pbar collisions at sqrt{s} = 1.8 TeV at the Fermilab Tevatron Collider. The data, which correspond to an integrated luminosity of 110.2 pb^-1, were collected with the Dzero detector from 1992 to 1996. We find a top quark mass of 178.5 + 13.7 (stat) + 7.7(syst) GeV/c^2.

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