Top-Higgs Yukawa Coupling Measurement at a Linear e+e- Collider

TL;DR

This work assesses the feasibility of directly measuring the top-Higgs Yukawa coupling g_{ttH} at a future 800 GeV e+e- linear collider using the ttH process with a 120 GeV Higgs. It emphasizes realistic simulation, including backgrounds, detector effects, and multivariate analyses across both semileptonic and hadronic ttH decay channels, to optimize signal sensitivity. The study demonstrates that, with 1000 fb⁻¹, a combined precision of about 5.5% on g_{ttH} is achievable, with the statistical component around 4.2%, highlighting the value of a realistic, multi-channel approach and robust background handling for precision Higgs-fermion coupling measurements.

Abstract

A feasibility study of the measurement of the top-Higgs Yukawa coupling at a future linear e+e- collider operating at sqrt(s)=800 GeV is presented. As compared to previous existing studies, much effort has been put in a ``realistic simulation'' by including irreducible+reducible backgrounds, realistic detector effects and reconstruction procedures and finally, a multivariate analysis. Both hadronic and semileptonic decay channels have been considered.

Figures (14)

• Figure 1: Tree level diagrams diagrams contributing to the process $t\bar{t}H$.
• Figure 2: Total cross-section for $t\bar{t}H$ at lowest order, for $m_t = 175$ GeV and $M_H = 120$ GeV, as a function of the center-of-mass energy. In (a) the two contributions: $H$ off the $t$ (dashed) and $H$ off the $Z$ (dotted) are explicited. The effect of radiative processes in the initial state (initial state radiation and beamstrahlung) on the total cross-section is illustrated in (b).
• Figure 3: Sensitivity of the total cross-section on the top-Higgs Yukawa coupling as a function of the center-of-mass energy for $M_H = 120$ GeV and including radiative effects: (a) "sensitivity factors", (b) statistical uncertainty for an ideal selection assuming an integrated luminosity of 1000 fb$^{-1}$.
• Figure 4: Track 3D impact parameter significance for $Z$ hadronic events at $\sqrt{s}$=100 GeV.
• Figure 5: b-tagging efficiency and purity for $t\bar{t}H \to q\bar{q}q\bar{q}b\bar{b}b\bar{b}$ events as a function of the lifetime probability cut.