Search for neutralinos in e+e- reactions at the L3 experiment

The present thesis deals with the search for neutralinos, which are predicted in the framework of the minimal supersymmetric standard model (MSSM). The lightest of the neutralinos is favorized as the lightest supersymmetric particle. With it, how far this assumption is confirmed, all decay chains of other SUSY particles would end. The data, on which the experimental studies are based, were collected in the year 1990 with the L3 detector at the e+e--storage ring LEP at a c.m. energy around 91 GeV. In them no hint on the existence of SUSY particles is found, whereby a) deviations of the decay width of the Z0 boson from the standard-model prediction and b) in hadronic final states directly detectable neutralinos are looked for. The results are presented in form of regions in the parameter space of the MSSM - tan β, M2, μ- as well as masses for the lightest neutralinos in dependence on tan β, which are excluded with 95% c.l. Quite generally it can be stated, that a neutralino with a mass of less than 19 geV for tan β>3 is no more allowed in the framework of the MSSM. (orig.)