Precision measurements of threshold chargino production

We analyze the prospects at a muon collider for measuring chargino masses in the ${\mu }^{+}{\mu }^{-}\to {\tilde{\chi }}^{+}{\tilde{\chi }}^{-}$ processes in the threshold region. We find that a measurement of the lightest chargino mass to better than 200 MeV is possible with 100~fb${}^{-1}$ luminosity. The muon sneutrino mass can also be simultaneously measured to a few GeV.