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

Abstract

We study the expected sensitivity to measure the branching ratio of Higgs boson decays to invisible particles at a future circular e^+e^-collider (FCC-ee) in the process e^+e^-rightarrow HZ with Zrightarrow 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. The minimum branching ratio for a 5sigma observation after 3.5 ab^{-1} of data taking is 1.7pm 0.1%(stat+syst) . The branching ratio exclusion limit at 95% CL is 0.63 pm 0.22%((stat+syst)).