Measurement of $\sigma(e^+e^- \to HZ) \times {\cal B}r(H \to ZZ^*)$ at the 250 GeV ILC

TL;DR

This study measures the cross section times branching ratio for the process e+e- to HZ with H to ZZ* at 250 GeV ILC, using detailed simulations to explore different decay channels, polarizations, and a model-independent Higgs width determination.

Contribution

It introduces a detailed simulation-based analysis of Higgs to ZZ* decays at the ILC, including a novel model-independent method for measuring the Higgs width.

Findings

Measured cross section times branching ratio with high precision.

Analyzed four decay channels with different polarizations.

Proposed a model-independent Higgs width measurement method.

Abstract

We report on studies of the $e^+e^- \to HZ$ process with the subsequent decay of the Higgs boson $H \to Z Z^\star$, where the $Z Z^\star$ combination is reconstructed in the final states with two jets and two leptons. The analysis is performed using Monte Carlo data samples obtained with detailed ILD detector simulation assuming the integrated luminosity 2 ab$^{-1}$, the beam polarizations ${\cal{P}}_{e^-e^+} = (-0.8, +0.3)$, and the center-of-mass energy $\sqrt{s}$ = 250 GeV. The analysis is also repeated for the case of two 0.9 ab$^{-1}$ data samples with polarizations ${\cal{P}}_{e^-e^+} = (\mp0.8, \pm0.3)$. The process is measured in four decay channels, which correspond to two combinations for the Higgs final states and two decay modes of the directly produced $Z$ boson, $Z \to q \bar{q}$ and $Z \to \nu \bar{\nu}$. To obtain the Higgs boson mass distributions, we used the variables $M(jj\ell\ell)$ and $M_{\Delta} = M(jj\ell\ell) - M(jj) + M(Z_{\rm nom})$, where $M(Z_{\rm nom})$ = 91.2 GeV. Contributions of the potential background processes are taken into account based on the available MC event samples. We propose a model-independent method for obtaining the width of the Higgs boson using the measurement of the $e^+e^- \to HZ$ process.