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 $\sigma(\gamma_-)/\sigma(\gamma_+)$ 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 $M_W^2\cos2\beta$ in a model-independent way. 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.