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

Abstract

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 √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 tt̄ 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(|ΔY| > 0) - N(|ΔY| < 0))/(N(|ΔY| > 0) + N(|ΔY| < 0)). To allow comparisons with theory calculations, a Bayesian unfolding technique is applied to correct the measured |ΔY| 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) and 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 A C = 0.006. © Owned by the authors 2012.