Measurement of the Higgs boson mass and e+e−→ZH cross section using Z→μ+μ− and Z→e+e− at the ILC

Abstract

This paper presents a full simulation study of the measurement of the production cross section (${\ensuremath{\sigma}}_{ZH}$) of the Higgsstrahlung process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}ZH$ and the Higgs boson mass (${M}_{\mathrm{H}}$) at the International Linear Collider (ILC), using events in which a Higgs boson recoils against a $Z$ boson decaying into a pair of muons or electrons. The analysis is carried out for three center-of-mass energies $\sqrt{s}=250$, 350, and 500 GeV, and two beam polarizations ${e}_{\mathrm{L}}^{\ensuremath{-}}{e}_{\mathrm{R}}^{+}$ and ${e}_{\mathrm{R}}^{\ensuremath{-}}{e}_{\mathrm{L}}^{+}$, for which the polarizations of ${e}^{\ensuremath{-}}$ and ${e}^{+}$ are $(P{e}^{\ensuremath{-}},P{e}^{+})=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}80%,+30%)$ and ($+80%$, $\ensuremath{-}30%$), respectively. Assuming an integrated luminosity of $250\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ for each beam polarization at $\sqrt{s}=250\text{ }\text{ }\mathrm{GeV}$, where the best lepton momentum resolution is obtainable, ${\ensuremath{\sigma}}_{ZH}$ and ${M}_{\mathrm{H}}$ can be determined with a precision of 2.5% and 37 MeV for ${e}_{\mathrm{L}}^{\ensuremath{-}}{e}_{\mathrm{R}}^{+}$ and 2.9% and 41 MeV for ${e}_{\mathrm{R}}^{\ensuremath{-}}{e}_{\mathrm{L}}^{+}$, respectively. Regarding a 20 year ILC physics program, the expected precisions for the HZZ coupling and ${M}_{\mathrm{H}}$ are estimated to be 0.4% and 14 MeV, respectively. The event selection is designed to optimize the precisions of ${\ensuremath{\sigma}}_{ZH}$ and ${M}_{\mathrm{H}}$ while minimizing the bias on the measured ${\ensuremath{\sigma}}_{ZH}$ due to discrepancy in signal efficiencies among Higgs decay modes. For the first time, model independence has been demonstrated to a sub-percent level for the ${\ensuremath{\sigma}}_{ZH}$ measurement at each of the three center-of-mass energies. The results presented show the impact of center-of-mass energy and beam polarization on the evaluated precisions and serve as a benchmark for the planning of the ILC run scenario.