Study the effect of beam energy spread and detector resolution on the search for Higgs boson decays to invisible particles at a future e$^+$e$^-$ circular collider

TL;DR

This study evaluates how beam energy spread and detector resolution affect the sensitivity of future e+e- colliders in detecting Higgs decays to invisible particles, providing estimates for observation and exclusion limits.

Contribution

It analyzes the impact of beam energy spread and detector resolution on Higgs invisible decay searches at FCC-ee, comparing two detector concepts and quantifying sensitivity.

Findings

Minimum branching ratio for 5σ detection: 1.7%

95% CL exclusion limit: 0.63%

Impact of detector resolution on sensitivity is significant

Abstract

We study the expected sensitivity to measure the branching ratio of Higgs boson decays to invisible particles at a future circular \epem collider (FCC-ee) in the process $e^+e^-\to HZ$ with $Z\to \ell^+\ell^-$ ($\ell=e$ or $\mu$) using an integrated luminosity of 3.5 ab$^{-1}$ at a center-of-mass energy $\sqrt{s}=240$ GeV. The impact of the energy spread of the FCC-ee beam and of the resolution in the reconstruction of the leptons is discussed. %Two different detector concepts are considered: a detector corresponding to the CMS reconstruction performances and the expected design of the ILC detector. The minimum branching ratio for a $5\sigma$ observation after 3.5ab$^{-1}$ of data taking is $1.7\pm 0.1\%(stat+syst) $. The branching ratio exclusion limit at 95\% CL is $0.63 \pm 0.22\%((stat+syst))$.