A study of top-quark Yukawa coupling measurement in e+e- -> t tbar H at sqrt(s) = 500 GeV

TL;DR

This study evaluates the potential to measure the top-quark Yukawa coupling at 500 GeV in e+e- collisions, considering QCD threshold effects, and finds promising significance levels for detection in future collider experiments.

Contribution

It demonstrates that QCD threshold corrections significantly enhance the t tbar H production cross section at 500 GeV, enabling feasible measurement at this energy.

Findings

Observation significance of 4.1 sigma without polarization.

Observation significance of 5.4 sigma with polarization.

QCD threshold effects increase cross section at 500 GeV.

Abstract

We report on the feasibility of measuring the top Yukawa coupling in the process: $e^+e^-\to t\bar{t}H$. This measurement is crucial to test the mass generation mechanism for matter particles. Since the cross section for this process attains its maximum around $\sqrt{s}=700 $GeV, most of the past studies were done assuming this energy region. It has been pointed out, however, that the QCD threshold correction enhances the cross section significantly and might enable its measurement at $\sqrt{s}=500 $GeV, which will be accessible already in the first phase of the ILC project. We have implemented this threshold enhancement into our $t\bar{t}H$ event generator and carried out Monte Carlo simulations. Our results show that $t\bar{t}H$ events can be observed with a significance of $4.1\,\sigma$ with no beam polarization and $5.4 \sigma$ with the $e^-$ and $e^+$ beam polarization combination: $(-0.8,+0.3)$.