Measurement of top quark polarization in top-antitop events from proton-proton collisions at √s = 7 TeV using the ATLAS detector

This Letter presents measurements of the polarization of the top quark in top-antitop quark pair events, using 4.7  fb −1 of proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at √s = 7  TeV. Final states containing one or two isolated leptons (electrons or muons) and jets are considered. Two measurements of αℓP , the product of the leptonic spin-analyzing power and the top quark polarization, are performed assuming that the polarization is introduced by either a CP conserving or a maximally CP violating production process. The measurements obtained, αℓPCPC = −0.035 ± 0.014(stat) ± 0.037(syst) and αℓPCPV = 0.020 ± 0.016(stat) + 0.013 − 0.017 (syst), are in good agreement with the standard model prediction of negligible top quark polarization.