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.