Optimized probes of $CP$-odd effects in the $t\bar{t}h$ process at hadron colliders

Abstract

We use machine learning (ML) and non-ML techniques to study optimized $CP$-odd observables, directly and maximally sensitive to the $CP$-odd $i\tilde{\kappa }\bar{t}{\gamma }^{5}th$ interaction at the LHC and prospective future hadron colliders using the final state with a Higgs boson and a top quark pair, $pp\to t\bar{t}h$, followed by semileptonic $t$ decays. We perform phase-space optimization of manifestly $CP$-odd observables ($\mathbf{\omega }$), sensitive to the sign of $\tilde{\kappa }$, and constructed from experimentally accessible final state momenta. We identify a simple optimized linear combination $\mathbf{\alpha }\cdot \mathbf{\omega }$ that gives similar sensitivity as the studied fully fledged ML models. Using $\mathbf{\alpha }\cdot \mathbf{\omega }$ we project the expected sensitivities to $\tilde{\kappa }$ at HL-LHC, HE-LHC, and FCC-hh.

Comments: As published