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1.
  • Abazov, V. M., et al. (författare)
  • Direct observation of the strange b baryon Xi(-)(b)
  • 2007
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:5, s. 052001
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We report the first direct observation of the strange b baryon Xi(-)(b)(Xi) over bar (+)(b)). We reconstruct the decay Xi(-)(b)--&gt;J/psi Xi(-), with J/psi--&gt;mu(+)mu(-), and Xi(-)--&gt;Lambda pi(-)--&gt;p pi(-)pi(-) in p (p) over bar collisions at root 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)--&gt;J/psi Lambda, we measure the relative rate sigma(Xi(-)(b))xB(Xi(-)(b)--&gt;J/psi Xi)/ sigma(Lambda(b))xB(Lambda(b)--&gt;J/psi Lambda) = 0.28 +/- 0.09(stat)(-0.08)(+0.09)(syst).</p>
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2.
  • Abazov, V. M., et al. (författare)
  • Double parton interactions in gamma+3 jet events in p(p)over-bar collisions at root s=1.96 TeV
  • 2010
  • Ingår i: Physical Review D. - 1550-7998. ; 81:5, s. 052012
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We have used a sample of gamma + 3 jets events collected by the D0 experiment with an integrated luminosity of about 1 fb(-1) to determine the fraction of events with double parton scattering (f(DP)) in a single p (p) over bar collision at root s = 1.96 TeV. The DP fraction and effective cross section (sigma(eff)), a process-independent scale parameter related to the parton density inside the nucleon, are measured in three intervals of the second (ordered in p(T)) jet transverse momentum p(T)(jet2) within the range 15 &lt;= p(T)(jet2) &lt;= 30 GeV. In this range, f(DP) varies between 0.23 &lt;= f(DP) &lt;= 0.47, while sigma(eff) has the average value sigma(ave)(eff) = 16.4 +/- 0.3(stat) +/- 2.3(syst) mb.</p>
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3.
  • Abazov, V. M., et al. (författare)
  • Evidence for an Anomalous Like-Sign Dimuon Charge Asymmetry
  • 2010
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 105:8, s. 081801
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We measure the charge asymmetry A =(N++ -N--)/(N++ + N--) of like-sign dimuon events in 6.1 fb(-1) of p (p) over bar collisions recorded with the D0 detector at a center-of-mass energy root s = 1: 96 TeV at the Fermilab Tevatron collider. From A we extract the like-sign dimuon charge asymmetry in semileptonic b-hadron decays: A(sl)(b) = -0.009 57 +/- 0.00251(stat) +/- 0.001 46(sys). It differs by 3.2 standard deviations from the standard model prediction A(sl)(b)(SM) = (-2.3(-0.6)(+0.5)) x 10(-4), and provides first evidence of anomalous CP violation in the mixing of neutral B mesons.</p>
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4.
  • Abazov, V. M., et al. (författare)
  • Evidence for an anomalous like-sign dimuon charge asymmetry
  • 2010
  • Ingår i: Physical Review D. - 1550-7998. ; 82:3, s. 032001
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We measure the charge asymmetry A of like-sign dimuon events in 6.1 fb(-1) of p (p) over bar collisions recorded with the D0 detector at a center-of-mass energy root s = 1.96 TeV at the Fermilab Tevatron collider. From A, we extract the like-sign dimuon charge asymmetry in semileptonic b-hadron decays: A(sl)(b) = -0.00957 +/- 0.00251 (stat) +/- 0.00146 (syst). This result differs by 3.2 standard deviations from the standard model prediction A(sl)(b)(SM) = (-2.3(0.6)(+0.5)) x 10(-4) and provides first evidence of anomalous CP violation in the mixing of neutral B mesons.</p>
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5.
  • Abazov, V. M., et al. (författare)
  • Evidence for the Decay B-s(0)-&gt;(DsDs(*))-D-(*) and a Measurement of Delta Gamma(CP)(s)/Gamma(s)
  • 2009
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:9, s. 091801
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We search for the semi-inclusive process B-s(0)-&gt;(DsDs(*))-D-(*) using 2.8 fb(-1) of pp collisions at s=1.96 TeV recorded by the D0 detector operating at the Fermilab Tevatron Collider. We observe 26.6 +/- 8.4 signal events with a significance above background of 3.2 standard deviations yielding a branching ratio of B(B-s(0)-&gt;(DsDs(*))-D-(*))=0.035 +/- 0.010(stat.)+/- 0.011(syst.). Under certain theoretical assumptions, these double-charm final states saturate CP-even eigenstates in the B-s(0) decays resulting in a width difference of Delta Gamma(CP)(s)/Gamma(s)=0.072 +/- 0.021(stat.)+/- 0.022(syst.).</p>
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6.
  • Abazov, V. M., et al. (författare)
  • Measurement of direct photon pair production cross sections in p(p)over-bar collisions at root s=1.96 TeV
  • 2010
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 690:2, s. 108-117
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We present a measurement of direct photon pair production cross sections using 4.2 fb(-1) of data collected with the DO detector at the Fermilab Tevatron p (p) over bar Collider. We measure single differential cross sections as a function of the diphoton mass, the transverse momentum of the diphoton system, the azimuthal angle between the photons, and the polar scattering angle of the photons. In addition, we measure double differential cross sections considering the last three kinematic variables in three diphoton mass bins. The results are compared with different perturbative QCD predictions and event generators. (C) 2010 Elsevier B.V. All rights reserved.</p>
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7.
  • Abazov, V. M., et al. (författare)
  • Measurement of the t-channel single top quark production cross section
  • 2010
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 682:4-5, s. 363-369
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The DO 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 p (p) over bar 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(-0.80)(+0.94) pb for the t-channel and 1.05 +/- 0.81 pb for the s-channel. The measured t-channel result is found to have a significance of 4.8 standard deviations and is consistent with the standard model prediction.</p>
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8.
  • Abazov, V. M., et al. (författare)
  • Measurement of Z/gamma* plus jet plus X angular distributions in p(p)over-bar collisions at root s=1.96 TeV
  • 2010
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 682:4-5, s. 370-380
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We present the first measurements at a hadron collider of differential cross sections for Z/gamma* + jet + X production in Delta phi(Z. jet), vertical bar Delta y(Z, jet)vertical bar and vertical bar y(boost)(Z + jet)vertical bar. 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.</p>
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9.
  • Abazov, V. M., et al. (författare)
  • Search for charged Higgs bosons in top quark decays
  • 2009
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 682:3, s. 278-286
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We present a search for charged Higgs bosons in top quark decays. We analyze the e + jets, mu + jets, ee, e mu, mu mu, tau e and tau mu final states from top quark pair production events, using data from about 1 fb (1) of integrated luminosity recorded by the DO 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 -&gt; H(+)b) for all these models. We use two methods, one where the t (t) over bar production cross section is fixed, and one where the cross section is fitted simultaneously with B(t -&gt; H(+)b). Based on the extracted limits, we exclude regions in the charged Higgs boson mass and tan beta parameter space for different scenarios of the minimal supersymmetric standard model.</p>
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10.
  • Abazov, V. M., et al. (författare)
  • Search for Higgs Boson Production in Dilepton and Missing Energy Final States with 5.4 fb(-1) of p(p)over-bar Collisions at root s=1.96 TeV
  • 2010
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:6, s. 061804
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>A search for the standard model Higgs boson is presented using events with two charged leptons and large missing transverse energy selected from 5.4 fb(-1) of integrated luminosity in p ($) over bar collisions at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron collider. No significant excess of events above background predictions is found, and observed (expected) upper limits at 95% confidence level on the rate of Higgs boson production are derived that are a factor of 1.55 (1.36) above the predicted standard model cross section at m(H) = 165 GeV.</p>
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