Sparticle production in electron-photon collisions

We explore the potential of electron-photon colliders to measure fundamental supersymmetry parameters via the processes eγ→ẽχ̃0 (selectron-neutralino) and eγ→ν̃χ̃− (sneutrino-chargino). Given the χ̃0 and χ̃− masses from e+e− and hadron collider studies, cross section ratios σ(γ−)/σ(γ+) for opposite photon helicities determine the ν̃L, ẽL and ẽR masses, independent of the sparticle branching fractions. The difference mν̃L2−mẽL2 measures MW2cos2β in a model-independent way. The ẽL and ẽR masses test the universality of soft supersymmetry breaking scalar masses. The cross section normalizations provide information about the gaugino mixing parameters.