Precision W-boson and Higgs boson mass determinations at muon colliders

Precise determinations of the masses of the W boson and of the top quark could stringently test the radiative structure of the Standard Model (SM) or provide evidence for new physics. We analyze the excellent prospects at a muon collider for measuring M_W and m_t in the W⁺W^- and ZH threshold regions. With an integrated luminosity of 10 (100) fb^-1, the W-boson mass could be measured to a precision of 20 (6) MeV, provided that theoretical and experimental systematics are understood. A measurement of ∆M_W=6 MeV would constrain the mass of a ∼100 GeV Higgs to about ±10 GeV. We demonstrate that a measurement at future colliders of the Bjorken process With an integrated luminosity of 100 fb^-1 it is possible to measure the Standard Model Higgs mass to within 45 MeV at a μ⁺μ^- collider for m_h=100 GeV.