Measurement of Top Quark Polarization in Top-Antitop Events from Proton-Proton Collisions at $\sqrt{s}$ = 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 $\alpha_l P$, 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 (CPC) or a CP violating (CPV) production process. The measurements obtained, $\alpha_l P_{CPC} = −0.035± 0.014(stat) ± 0.037(syst)$ and $\alpha_l P_{CPV} = 0.020 ± 0.016(stat)^{+0.013} _{-0.017}(syst)$, are in good agreement with the Standard Model prediction of negligible top quark polarization.