Search for charginos, neutralinos and gravitinos at LEP

An update of the searches for charginosand neutralinosin DELPHI is presented, based mainly on recent data collected at centre-of-mass energies of 161 GeV and 172 GeV. No signal is found. For a sneutrino with mass above 300 GeV/c2 and a mass difference between the charginoand the lightest neutralinoabove 10 GeV/c2, the lower limit at 95% confidence level on the charginomass ranges from 84.3 GeV/c2 to the kinematical limit (86.0 GeV/c2), depending on the mixing parameters. The limit decreases for lower chargino- neutralinomass differences. The limit in the case of a light sneutrino is 67.6 GeV/c2, provided that that there is no light sneutrino with a mass within 10 GeV/c2 below the charginomass. Upper limits on neutralino pair productioncross-sections of about a picobarn are derived. The (μ,M2) domain excluded in the MSSM-GUT scenario is determined by combining the neutralinoand charginosearches. These results imply a limit on the mass of the lightest neutralinowhich, for a heavy sneutrino, is constrained to be above 24.9 GeV/c2 for tans >- 1. The search has also been extended to the case where the lightest neutralinois unstable and decays into a photon and a gravitino. imply a limit on the mass of the lightest neutralinowhich, for a heavy sneutrino, is constrained to be above 24.9 GeV/c2 for tans >- 1. The search has also been extended to the case where the lightest neutralinois unstable and decays into a photon and a gravitino.