Probing the CP properties of top Yukawa coupling at an $e^+e^-$ collider

TL;DR

This paper investigates how CP violation in the top Yukawa coupling affects the process e+e- -> h t t̄, analyzing angular distributions and asymmetries to enhance detection sensitivity at future colliders.

Contribution

It provides a comprehensive analytical framework for production and decay angular distributions, highlighting improved sensitivity to CP violation at higher collider energies.

Findings

CP-violating asymmetries in angular distributions are identified.

Decay angular correlations significantly enhance CP violation detection.

Increasing collider energy from 500 GeV to 550 GeV improves sensitivity.

Abstract

We study consequences of CP violation in the $ht\bar{t}$ Yukawa coupling through the process $e^+e^- \to$ $h(125)t\bar{t}$. The helicity amplitudes are calculated in the $t\bar{t}$ rest frame, where the initial $e^+e^-$ current and the final Higgs boson have the same three-momentum. CP-violating asymmetries appear not only in the azimuthal angle between the $e^+e^-$ plane and the $t\bar{t}$ plane about the Higgs momentum direction, but also in the correlated decay angular distributions of $t$ and $\bar{t}$. Complete description of the production and decay angular distributions are obtained analytically, including both leptonic and hadronic decays of $t$ and $\bar{t}$. We study the ultimate sensitivity to the CP-violating $ht\bar{t}$ coupling at a few center-of-mass energies. Our analysis shows that the possibility of discovering CP violating $ht\bar{t}$ coupling improves significantly by studying $t\bar{t}$ decay angular correlations, and more importantly, by increasing its energy upgrade target from $\sqrt{s} = 500$ GeV to 550 GeV.