Both cross sections are measured in a fiducial kinematic region within the ATLAS acceptance. The result for extra HF production is quoted as a ratio ( R HF) of the cross section for t t ¯ + HF production to the cross section for t t ¯ production with at least one additional jet. The result of the fit shows that 79 ± 14 ( stat ) ± 22 ( syst ) of the 105 selected extra b-tagged jets originate from HF quarks, 3 standard deviations away from the hypothesis of zero t t ¯ + HF production. 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 dominant background to t t ¯ + HF in this sample is t t ¯ + jet events in which a light-flavor jet is misidentified as a heavy-flavor jet. The presence of additional HF ( b or c) quarks in the t t ¯ sample is inferred by looking for events with at least three b-tagged jets, where two are attributed to the b quarks from the t t ¯ decays and the third to additional HF production. ![]() The data set 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. Using a sample of dilepton top-quark pair ( t t ¯) candidate events, a study is performed of the production of top-quark pairs together with heavy-flavor (HF) quarks, the sum of t t ¯ + b + X and t t ¯ + c + X, collectively referred to as t t ¯ + HF.
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