This Letter presents measurements of the polarization of the top quark in top-antitop quark pair events, using 4:7 fb–1of 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.
Aad, G., Abajyan, T., Abbott, B., Abdallah, J., Khalek, S. A., Abdinov, O., … Zwalinski, L. (2013). Measurement of top quark polarization in top-antitop events from proton-proton collisions at √s = 7 TeV using the ATLAS detector. Physical Review Letters, 111(23). https://doi.org/10.1103/PhysRevLett.111.232002