Measurement of the charge asymmetry in dileptonic decay of top quark pairs in pp collisions at √s = 7 TeV using the ATLAS detector

A measurement of the top-antitop charge asymmetry in the dilepton channel (ee,emu and mumu) is presented using data corresponding to an integrated luminosity of 4.71 fb−1 of pp collisions at √s = 7 TeV collected by the ATLAS detector. Selected events are required to have exactly two leptons (electron or muon), large missing transverse momentum and at least two jets. A likelihood based on the calculation of the leading order matrix-element is used to reconstruct the tt event topology. After background subtraction, a calibration is applied to correct for acceptance and detector effects. Two charge asymmetry observables are studied: one based on the lepton rapidities A_C(ll) and one based on the reconstructed tt final state A_C(tt). Combining the ee, emu and mumu channels, the lepton-based asymmetry is measured to be: A_C(ll) = 0.023 ± 0.012 (stat.) ± 0.008 (syst.) in agreement with the Standard Model prediction of A_C(ll) = 0.004 ± 0.001. Similarly, the tt-based charge asymmetry is measured to be: A_C(tt) = 0.057 ± 0.024 (stat.) ± 0.015 (syst.) in agreement with the Standard Model prediction of A_C(tt) = 0.006 ± 0.002. A combination with the previous top-antitop charge asymmetry measurement with the ATLAS detector in the single lepton channel is also presented.