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

TL;DR

This paper investigates the CP properties of the top quark Yukawa coupling in $t\bar{t}h$ events at the 13 TeV LHC, using angular distributions and asymmetries to distinguish between CP-even, CP-odd, and mixed scenarios, providing expected limits on the coupling.

Contribution

It introduces a phenomenological analysis of the CP nature of the top Yukawa coupling using $t\bar{t}h$ events with detailed simulation and reconstruction, exploring sensitivity to CP-mixing angles.

Findings

Angular distributions can probe CP nature effectively.

Asymmetries remain sensitive after detector effects.

Expected limits vary with luminosity and CP-mixing.

Abstract

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 $h\rightarrow b\bar b$ 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 $t\bar th$ 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.