Measuring the ratio of $HWW$ and $HZZ$ couplings through $W^+W^-H$ production

TL;DR

This paper proposes a method to measure the ratio of Higgs couplings to W and Z bosons via $W^+W^-H$ production at future $e^+e^-$ colliders, providing a way to test the Higgs boson's origin.

Contribution

It introduces a novel approach to determine the $HWW$ and $HZZ$ coupling ratio through interference effects in $W^+W^-H$ production at future colliders.

Findings

Feasibility of measuring the coupling ratio at a 500-GeV ILC.

Enhanced sensitivity when combining with HL-LHC $HZZ$ measurements.

Potential to discriminate from the Standard Model value.

Abstract

For a generic Higgs boson, measuring the relative sign and magnitude of its couplings with the $W$ and $Z$ bosons is essential in determining its origin. Such a test is also indispensable for the 125-GeV Higgs boson. We propose that the ratio of the $HWW$ and $HZZ$ couplings $\lambda_{WZ}$ can be directly determined through the $W^+W^-H$ production, where $H$ denotes a generic Higgs boson, owing to the tree-level interference effect. While this is impractical at the LHC due to the limited sensitivity, it can be done at future $e^+e^-$ colliders, such as a 500-GeV ILC with the beam polarization $P(e^-,e^+)=(-0.8,+0.3)$ in the $jj\ell^{\pm}bb$ and $\ell^{\pm}\ell^{\pm}\ell^{\mp}jj$ channels. The discovery potential of a general ratio and the power to discriminate it from the SM value are studied in detail. Combining the cross section of $e^+e^-\to W^+ W^- H$ with the measurements of $HZZ$ coupling at the HL-LHC, one can further improve the sensitivity of $\lambda_{WZ}$.