A study of heavy flavor quarks produced in association with top quark pairs at $sqrts$ = 7 TeV using the ATLAS detector

Abstract

Using a sample of dilepton top-quark pair (ttbar) candidate events, a study is performed of the production of top-quark pairs together with heavy-flavor (HF) quarks, ttbar _s16 b _s16 X or ttbar _s16 c _s16 X, collectively referred to as ttbar _s16 HF. The dataset used corresponds to an integrated luminosity of 4.7 fb^-1 of proton--proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The dominant background to ttbar _s16 HF in this sample is ttbar _s16 jet events in which a light-flavor jet is misidentified as a heavy-flavor jet. To determine the heavy and light-flavor content of the additional b-tagged jets, a fit to the vertex mass distribution of b-tagged jets in the sample is performed. The result for extra HF production is quoted as a ratio (R_HF) of the cross section for ttbar _s16 HF production to the cross section for ttbar production with at least one additional jet. Both cross sections are measured in a fiducial kinematic region within the ATLAS acceptance. R_HF is measured to be [7.1 _s16/- 1.3 (stat.) _s165.3/-2.0 (syst.)] % for jets with pt > 25 GeV and |eta| < 2.5, compared to the leading-order QCD Standard Model expectation of [3.4 _s16/- 1.1] %.