Measurement of the charge asymmetry in top quark pair production in pp collisions at √s = 7 TeV using the ATLAS detector

We present a measurement of the charge asymmetry in top-antitop production using data corresponding to an integrated luminosity of 0.70 fb−1 of proton-proton collisions at sqrt (s) = 7 TeV collected by the ATLAS detector. The top pair events decaying semileptonically (lepton+jets channel) to either an electron or muon, missing transverse energy and at least four jets are selected. The reconstruction of the ttbar events was performed using a kinematic likelihood approach. The difference of absolute values of top and antitop rapidities is used to define the charge asymmetry: Ac = (N(|∆y|>0) - N(|∆y|<0) ) / (N(|∆y|>0) + N(|∆y|<0)). To allow comparisons with theory calculations, a Bayesian unfolding technique is applied to correct the measured |∆y| distributions for acceptance and detector effects. The top charge asymmetry in both channels (e and mu) after correction is measured to be: AC = −0.009 ± 0.023 (stat.) ± 0.032 (syst.) (e+jets channel) AC = −0.028 ± 0.019 (stat.) ± 0.022 (syst.) (μ+jets channel) giving a combined result of : AC = −0.024 ± 0.016 (stat) ± 0.023 (syst) These results are compatible with the Standard Model predictions of Ac=0.006