Observing Virtual LSPs at LEP II

In the minimal supersymmetric extension of the Standard Model (MSSM) with $R$-parity conservation the possibility that the sneutrino and the second lightest neutralino decay dominantly into invisible channels and, in addition to the lightest neutralino, carry missing energy, is still open — both theoretically and experimentally. It is shown that for a large region of the parameter space allowed by {\rm LEP-I} data, these particles can contribute significantly to the process $e^{+}{e}^{-}⟶\gamma$ + {\rm nothing}. This signal, if it exists, can be easily detected at {\rm LEP-II} as an enhancement over the Standard Model or the conventional MSSM predictions.