Charge asymmetry in ttgamma production with the ATLAS experiment

The production of top quark pairs in association with a photon (t¯tγ) is a rare Standard Model process that provides direct access to the top quark-photon coupling. In t¯tγ production, the interferences of QCD and QED initial and final state radiation are expected to be sensitive to beyond Standard Model phenomena. Since it is not possible to isolate these interferences, an indirect way to measure them is via the differences of angular distribution of top and anti-top quarks in the process. The top quark pair charge asymmetry (Ac) is one such observable. In this presentation the first measurement of Ac in t¯tγ production in the single lepton channel with the full Run2 data collected at √s=13 TeV with the ATLAS experiment will be presented. Since the t¯tγ production has a small cross-section and there are large backgrounds present, a neural network based method is used for discrimination of the backgrounds. The Ac is measured in a fiducial phase space at the particle level using a profile likelihood unfolding method.