Measurement of the longitudinal polarization of the top quark in top-antitop events with the ATLAS experiment.

Abstract: "We perform two measurements of the product of the top quark polarization and the leptonic spin analyzing power ("alpha_l * P) assuming that the polarization is introduced by either a CP conserving (CPC) or CP violating (CPV) production process. We perform this analysis by analyzing top-antitop events collected in 4.7 fb^-1 of proton-proton collision data at 7 TeV center of mass energy, recorded with the ATLAS detector at the Large Hadron Collider. We use the single lepton channel, relying upon a kinematic likelihood fit to reconstruct the ttbar system. To extract alpha_l * P from the data, a fit using templates of partially polarized top quarks is performed. We also perform a combined fit with the dilepton channel. The single lepton and combined fits for alpha_l * P are within the Standard Model's expectation of negligible top quark polarization."