Method for measuring CP violation in top quark pair production at ATLAS

The Standard Model (SM) predicts that a large fraction of top quark pairs produced in 14 TeV center-of-mass pp collisions will have correlated helicities, and the number of tLt¯ L and tRt¯R pairs produced will be approximately equal. Unequal numbers of these pairs are an indication that CP symmetry is violated and there is new physics beyond the Standard Model. A method to measure CP violation in tt¯ pair production at the Large Hadron Collider is presented. In particular, the value of DeltaNLR = [sigma(t Lt¯L) - sigma(tRt¯ R)]/sigma(tt¯)TOT is found to be best measured in the lepton-plus-jets channel of tt¯ decay. In this channel, the top pair can be reconstructed and the angular distribution of the leptons with respect to the top quark momentum can be determined. The ATLAS experiment can measure DeltaNLR with a statistical uncertainty on the order of 3.5% using only 50 fb-1 of integrated luminosity. The sources of a number of systematic uncertainties were also studied. A method to detect CP violation in the dimuon decay channel using the PT asymmetry of oppositely charged muons was also investigated.