SEARCH FOR NEUTRALINOS IN Z-DECAYS

Abstract

We have searched for neutralinos produced via the reactions e(+)e(-) --> chi chi', and e(+)e(-) --> chi'chi', where the next-to lightest neutralino, chi', decays into the lightest neutralino, chi and either a photon or a fermion pair, Based on 1.8 X 10(6) hadronic Z decays collected with the L3 detector at LEP, no signal has been observed. We present upper limits of a few times 10(-5) on the branching ratios Z --> chi chi' and Z --> chi chi'. In the framework of the Minimial Supersymmetric Standard Model, we exclude a lightest chi with m(chi) less than 18 GeV, if either tan beta > 2 or the gluino mass m(g) > 100 GeV.