Enlightening a tiny difference: Measurement of top quark pair charge asymmetry in $t\bar{t}+\gamma$ production at LHC using the ATLAS detector at $\sqrt{s}$ = 13 TeV

A first measurement of the top quark pair charge asymmetry ($A_{C}$) is presented in top quark pair ($t\bar{t}$) production in association with a photon ($t\bar{t}\gamma$ production), using the data of ATLAS experiment with an integrated luminosity of 139 $fb^{-1}$ collected at proton-proton collisions of $\sqrt{s}=13$ TeV at the Large Hadron Collider at CERN. The measurement is performed using the semileptonic tt̄ decay channel in fiducial phase space at particle level using a profile likelihood unfolding method on the distribution of the difference between the absolute rapidity of the two top quarks. The $A_{C}$ is measured to be $-0.003 \pm 0.029$, in agreement with the Standard Model prediction. The measurement is expected to be more sensitive to potential new physics than the same measurement in tt̄ production. However, currently, it is limited by the available statistics and serves as a stepping stone for future analyses with more data.