Study of the $\cal{CP}$ properties of the top quark Yukawa interaction in $t\bar{t}H$ and $tH$ events with $H\to~\gamma\gamma$

These procedings present the first search for $\cal{CP}$-violation in the top Yukawa coupling using $t\bar{t}H$ and $tH$ production modes in the diphoton decay channel ($H\to\gamma\gamma$). The analysis is based on the 139~fb$^{-1}$ of proton-proton collision data at center-of-mass energy $\sqrt{s}$~=~13~\TeV\ recorded with the ATLAS detector at the Large Hadron Collider. Two separate set of selections are introduced to capture the full hadronic and leptonic decay of the $t\bar{t}$\ system each. This search is performed using a simultaneous fit to the $m_{\gamma\gamma}$ distribution in analysis categories defined to enhance signal over continuum background and also to separate the CP even and CP odd signal hypotheses.