Expected ${\boldsymbol H \xrightarrow{} {\boldsymbol{\mu^+\mu^-}}} $ measurement precision with ${\boldsymbol { e^{+}e^{-}}{\bf \xrightarrow{}}{ \boldsymbol{Z(q\bar{q})H}}}$ production at the CEPC

Abstract：

A search for the dimuon decay of the Standard Model Higgs boson is performed using Monte Carlo simulated events to mimic data corresponding to an integrated luminosity of 5.6 ab $ ^{-1} $ collected with the Circular Electron-Positron Collider detector in $ e^{+}e^{-} $ collisions at $ \sqrt{s}=240 $ GeV. This study investigates the $ e^{+}e^{-}\to ZH,\, $ $ Z\to q\bar{q},\,H\to {{\mu^+\mu^-}} $ process, and the expected significance considering only the statistical uncertainty in the data for a background-only hypothesis for a Higgs boson with a mass of 125 GeV is found to be 6.1 $ \sigma $ , corresponding to a precision of 19%. The systematic impacts from the background Monte Carlo statistical fluctuations are estimated to be negligible. Moreover, the dependence of the measurement accuracy on the muon momentum resolution of the CEPC detector is investigated. It is found that the muon momentum resolution must be better than 204 MeV to discover the $ H\to\mu\mu $ process at the nominal integrated luminosity. If the resolution is 100% worse than the designed parameter, the integrated luminosity must be greater than 7.2 ab $ ^{-1} $ to reach 5 $ \sigma $ significance.