Probing the CP nature of the Higgs coupling in $t\bar{t}h$ events at the LHC

The determination of the CP nature of the top quark Yukawa coupling is addressed in this phenomenological work, using $t\bar{t}h$ events at the $\sqrt{s}$ = 13 TeV LHC, with $h\to b\bar{b}$ and through the dilepton decay channel of $t\bar{t}$. Signal events were generated for pure $CP$-even, pure $CP$-odd and mixed-$CP$ coupling scenarios. Standard Model (SM) backgrounds were also considered. Angular distributions and asymmetries were studied and found to be potentially good probes to the $CP$ nature of the coupling, even after detector simulation and full event reconstruction using a kinematic fit. Expected limits to the $t\bar{t}h$ production cross-section times branching ratio were obtained for a range of top quark Yukawa $CP$-mixing angles and for different integrated luminosities of the LHC.