Observing virtual light supersymmetric particles 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 LEP-I data, these particles can contribute significantly to the process e+e− → γ + nothing. This signal, if it exists, can be easily detected at LEP-II as an enhancement over the Standard Model or the conventional MSSM predictions.