Sparticle Production in Electron-Photon Collisions

We explore the potential of electron-photon colliders to measure fundamental supersymmetry parameters via the processes $e\gamma \to \tilde{e}{\tilde{\chi }}^0$ (selectron-neutralino) and $e\gamma \to \tilde{\nu }{\tilde{\chi }}^{-}$ (sneutrino-chargino). Given the ${\tilde{\chi }}^0$ and ${\tilde{\chi }}^{-}$ masses from $e^{+}{e}^{-}$ and hadron collider studies, cross section ratios $\sigma ({\gamma }_{-})\mathrm{/}\sigma ({\gamma }_{+})$ for opposite photon helicities determine the ${\tilde{\nu }}_L$, ${\tilde{e}}_L$ and ${\tilde{e}}_R$ masses, independent of the sparticle branching fractions. The difference $m_{\tilde\nu_L}^2-m_{\tilde e_L}^2$measures$M_W^2\cos2\beta$inamodel-independentway\mathrm{.}The$\tilde e_L$and$\tilde e_R$ masses test the universality of soft supersymmetry breaking scalar masses. The cross section normalizations provide information about the gaugino mixing parameters.