Measurement of Top Quark Polarization in Top-Antitop Events from Proton-Proton Collisions at Using the ATLAS Detector

Abstract

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 ffiffi s p ¼ 7 TeV. Final states containing one or two isolated leptons (electrons or muons) and jets are considered. Two measurements of ‘P, 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, α_l P_CPC=-0.035±0.014(stat)_-^+ 0.037(syst) and α_l P_CPV=0.020±0.016(stat)_(-0.017)^(+0.013) (syst), are in good agreement with the standard model prediction of negligible top quark polarization.