We search for neutral heavy leptons that are isosinglets under the standard SU (2)l gauge group. Such neutral heavy leptons are expected in many extensions of the standard model. Three types of heavy leptons Ne, N^, NT associated with the three neutrino types v* have been directly searched for and no evidence for a signal has been found. We set the limit Br(Z° -► z//N*) < 3 x 10" 5 at the 95% CL for the mass range from 3 GeV up to m%.

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We present a study of 43 000 3-jet events from Z° boson decays. Both the measured jet energy distributions and the event orientation are reproduced by second order QCD. An alternative model with scalar gluons fails to describe the data.

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tralino production via t-channel exchange, which is of OCR Output a forward-backward tracking chamber, a high resolu assumed to be heavier than 45 so that the decays X' -+ Xh, XAand X' -» Xfff°°r esults are interpreted in the MSSM context as well as h° or A0, and charginos, gi are sufficiently large [5] hadronic Z decays collected in 1991 ---1993. TheseWe assume that the masses of the lightest higgs, search for neutralinos, which are based on 1.8 X 10 involving ·r leptons.We present the event selection and results of our small branching fraction, we did not investigate decays mass to charged leptons and quarks of charge -%e. with mx less than 18 GeV, if either tanB > 2 or the gluino mass mz-> 100 GeV.In the framework ofthe Minimal Supersymmetric Standard Model, we exclude a lightest X used to set upper limits of a few times 10'° on the branching ratios Z -• XX' and Z -» X'X'.hadronic Z decays collected with the L3 detector at LEP. Absence of any signal has been neutralino, X, and either a photon or a fcrmion pair. This analysis is based on 1.8 x 106XX' and e+e" -> X' X' , where the next-to lightest neutralino, X', decays into the lightest A search for neutralinos produced in Z decays has been performed via the reactions e+e" --> ABSTRACT L3 Collaboration