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31.
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32.
  • Abazov, V. M., et al. (författare)
  • Measurement of Spin Correlation in t(t)over-bar Production Using a Matrix Element Approach
  • 2011
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 107:3, s. 032001
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We determine the fraction of t (t) over bar events with spin correlation, assuming that the spin of the top quark is either correlated with the spin of the top antiquark as predicted by the standard model or is uncorrelated. For the first time we use a matrix-element-based approach to study t (t) over bar spin correlation. We use t (t) over bar -&gt; W(+)bW(-)(b) over bar -&gt; l(+)nu bl(-)(nu) over bar(b) over bar final states produced in p (p) over bar collisions at a center- of- mass energy root s = 1: 96 TeV, where l denotes an electron or a muon. The data correspond to an integrated luminosity of 5: 4 fb(-1) and were collected with the D0 detector at the Fermilab Tevatron collider. The result agrees with the standard model prediction. We exclude the hypothesis that the spins of the t (t) over bar are uncorrelated at the 97.7% C.L.</p>
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33.
  • Abazov, V. M., et al. (författare)
  • Measurement of spin correlation in t(t)over-bar production using dilepton final states
  • 2011
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 702:1, s. 16-23
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We measure the correlation between the spin of the top quark and the spin of the anti-top quark in t (t) over bar -&gt; W(+)bW(-)(b) over bar -&gt; l(+)vbl(-) (v) over bar(b) over bar final states produced in p (p) over bar collisions at a center of mass energy root s = 1.96 TeV, where l is an electron or muon. The data correspond to an integrated luminosity of 5.4 fb(-1) and were collected with the D0 detector at the Fermilab Tevatron collider. The correlation is extracted from the angles of the two leptons in the t and (t) over bar rest frames, yielding a correlation strength C = 0.10(-0.45)(+0.45). in agreement with the NLO QCD prediction within two standard deviations, but also in agreement with the no correlation hypothesis.</p>
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34.
  • Abazov, V. M., et al. (författare)
  • Measurement of t(t)over-bar production in the tau plus jets topology using p(p)over-bar collisions root s=1.96 TeV
  • 2010
  • Ingår i: PHYS REV D. - 1550-7998. ; 82:7, s. 071102
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We present a measurement of the t (t) over bar production cross section multiplied by the branching ratio to tau lepton decaying semihadronically (tau(h)) plus jets, sigma(p (p) over bar -&gt; t (t) over bar + X) center dot BR(t (t) over bar -&gt; tau(h) + jets), at a center of mass energy root s = 1.96 TeV using 1 fb(-1) of integrated luminosity collected with the D0 detector. Assuming a top quark mass of 170 GeV, we measure sigma(t (t) over bar) center dot BR tau h (+ j) = 0.60(-0.22)(+0.23)(stat)(-0.14)(+0.15)(syst) +/- 0.04(lumi) pb. In addition, we extract the t (t) over bar production cross section using the t (t) over bar -&gt; tau(h) + jets topology, with the result sigma(t (t) over bar) = 6.9(-1.2)(+1.2)(stat)(-0.7)(+0.8)(syst) +/- 0.4(lumi) pb. These findings are in good agreement with standard model predictions and measurements performed using other top quark decay channels.</p>
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35.
  • Abazov, V. M., et al. (författare)
  • Measurement of the anomalous like-sign dimuon charge asymmetry with 9 fb(-1) of p(p)over-bar collisions
  • 2011
  • Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 84:5, s. 052007
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We present an updated measurement of the anomalous like-sign dimuon charge asymmetry A(sl)(b) for semileptonic b-hadron decays in 9.0 fb(-1) of p (p) over bar collisions recorded with the D0 detector at a center-of-mass energy of root s = 1.96 TeV at the Fermilab Tevatron collider. We obtain A(sl)(b) = (-0.787 +/- 0.172(stat) +/- 0.093(syst)%. This result differs by 3.9 standard deviations from the prediction of the standard model and provides evidence for anomalously large CP violation in semileptonic neutral B decay. The dependence of the asymmetry on the muon impact parameter is consistent with the hypothesis that it originates from semileptonic b-hadron decays.</p>
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36.
  • Abazov, V. M., et al. (författare)
  • Measurement of the production fraction times branching fraction f(b -&gt; Lambda(b)) . B(Lambda(b) -&gt; J/psi Lambda)
  • 2011
  • Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 84:3, s. 031102
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The Lambda(b)(udb) baryon is observed in the decay Lambda(b) -&gt; J/psi Lambda using 6.1fb(-1) of p (p) over bar collisions collected with the D0 detector at root s = 1/96 TeV. The production fraction multiplied by the branching fraction for this decay relative to that for the decay B(0) -&gt; J/psi K(s)(0) is measured to be 0.345 +/- 0.034(stat) +/- 0.033(syst) +/- 0.003(PDG). Using the world average value of f(b -&gt; B(0)) . B(B(0) -&gt; J/psi K(s)(0) = (1.74 +/- 0.08) x 10(-5), we obtain f(b -&gt; Lambda(b)) . B(Lambda(b) -&gt; J/psi Lambda) = (6.01 +/- 0.60(stat) +/- 0.58(syst) +/- 0.28(PDG)) x 10(-5). This measurement represents an improvement in precision by about a factor of 3 with respect to the current world average.</p>
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37.
  • Abazov, V. M., et al. (författare)
  • Measurement of the t(t)over-bar production cross section using dilepton events in p(p)over-bar collisions
  • 2011
  • Ingår i: Physics Letters B. - 0370-2693 .- 1873-2445. ; 704:5, s. 403-410
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We present a measurement of the a production cross section sigma((u) over bar) in p (p) over bar collisions at root s = 1.96 TeV using 5.4 fb(-1) of integrated luminosity collected with the D0 detector. We consider final states with at least two jets and two leptons (ee, e mu, mu mu), and events with one jet for the e mu final state as well. The measured cross section is sigma((u) over bar) = 7.36(-0.79)(+0.90)(stat + syst) pb. This result combined with the cross section measurement in the lepton + jets final state yields sigma((u) over bar) = 7.56(-0.56)(+0.63)(stat + syst) pb, which agrees with the standard model expectation. The relative precision of 8% of this measurement is comparable to the precision of the latest theoretical calculations. (C) 2011 Elsevier B.V. All rights reserved.</p>
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38.
  • Abazov, V. M., et al. (författare)
  • Measurement of the top quark pair production cross section in the lepton plus jets channel in proton-antiproton collisions at root s=1.96 TeV
  • 2011
  • Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 84:1, s. 012008
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We present a measurement of the inclusive top quark pair production cross section in p (p) over bar collisions at root s = 1.96 TeV utilizing data corresponding to an integrated luminosity of 5.3 fb(-1) collected with the D0 detector at the Fermilab Tevatron Collider. We consider final states containing one high-p(T) isolated electron or muon and at least two jets, and we perform three analyses: one exploiting specific kinematic features of t (t) over bar events, the second using b-jet identification, and the third using both techniques to separate the t (t) over bar signal from the background. In the third case, we determine simultaneously the t (t) over bar cross section and the ratio of the production rates of W + heavy flavor jets and W + light flavor jets, which reduces the impact of the systematic uncertainties related to the background estimation. Assuming a top quark mass of 172.5 GeV, we obtain sigma(t (t) over bar) = 7.78(-0.64)(-0.77)pb. This result agrees with predictions of the standard model.</p>
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39.
  • Abazov, V. M., et al. (författare)
  • Measurement of the W boson helicity in top quark decays using 5.4 fb(-1) of p(p)over-bar collision data
  • 2011
  • Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 1550-7998. ; 83:3, s. 032009
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We present a measurement of the helicity of the W boson produced in top quark decays using t (t) over bar decays in the l + jets and dilepton final states selected from a sample of 5.4 fb(-1) of collisions recorded using the D0 detector at the Fermilab Tevatron p (p) over bar collider. We measure the fractions of longitudinal and right-handed W bosons to be f(0) = 0.669 +/- 0.102[+/- 0.078(stat.) +/- 0.065(syst.) +/- and f(+) = 0.023 +/- 0.053[+/- 0.041(stat.) +/- 0.034(syst.)], respectively. This result is consistent at the 98% level with the standard model. A measurement with f(0) fixed to the value from the standard model yields f(+) = 0.010 +/- 0.037[+/- 0.022(stat.) +/- 0.030(syst.).].</p>
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40.
  • Abazov, V. M., et al. (författare)
  • Measurement of the ZZ production cross section in p(p)over-bar collisions at root s=1.96 TeV
  • 2011
  • Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 84:1, s. 011103
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We present a new measurement of the production cross section sigma(p (p) over bar -&gt; ZZ) at a center-of-mass energy root s = 1.96 TeV, obtained from the analysis of the four charged lepton final state l(+)l(-)l'(+)l'-(l,l' = e or mu). We observe ten candidate events with an expected background of 0: 37 +/- 0: 13 events. The measured cross section sigma(p (p) over bar -&gt; ZZ) = 1.26(-0.37)(+0.47)(stat) +/- 0.14(syst) pb is in agreement with NLO QCD predictions. This result is combined with a previous result from the ZZ -&gt; l(+)l(-)v (v) over bar channel resulting in a combined cross section of sigma(p (p) over bar -&gt; ZZ) = 1.40(-0.37)(+0.43)(stat) +/- 0.14(syst) pb.</p>
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