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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%.

The results of the searches for neutral Higgs boson production in the process e+e---+ Z* Ho are reported, focusing on Higgs boson masses below 70 GeV. The data sample consists of three million hadronic Z" decays collected by the L3 experiment at LEP from 1991 through 1994. No signal is found leading to a lower limit on the mass of the Standard Model Higgs boson of 60.2 GeV at 95% C.L.These results are also interpreted in the framework of the General Two Doublet Model and limits on the nonstandard Higgs boson production through the process e + -e 4 Z* ho are set. A lower limit of 66.7 GeV at 95% CL. is obtained for the case where the Higgs decays into an invisible final state.

0370-2693r98r$ -see front matter q 1998 Elsevier Science B.V. All rights reserved.Ž . PII: S 0 3 7 0 -2 6 9 3 9 8 0 0 7 3 6 -9 ( ) M. Acciarri et al.r Physics Letters B 434 1998 169- AbstractWe analyse e q e y ™ ttg events using 100 pb y1 of data collected by the L3 experiment during the 1991-1995 LEP runs at the Z pole. From the energy of the photons and their isolation from the tau decay products, we determine the anomalous magnetic and electric dipole moments of the tau to be, respectively: a s 0.004 " 0.027 " 0.023; t d s 0.0 " 1.5 " 1.3 = 10 y16 e P cm. Ž .t This is a direct measurement of these t form factors at q 2 s 0. q 1998 Elsevier Science B.V. All rights reserved.

A search for exclusive decays of Bt and Bf mesons has been performed in the channels Bi 4 Jq, Bz + Jq Bi 4 Jr0 and Bg -_) J.R'. The data sample consisted of more than three and half million hadronic Z decays collected by the L3 experiment at LEP from 1991 through 1995. No candidate events have been observed for any of the modes thus determining upper limits at 90% confidence level: 3.2 x low4 on Br(Bj --+ Jr') and the first experimental limits: Br(J3: -+ Jv) < 1.2 x 10w3, Br(Bt -+ 57) < 3.8 x 10p3, Br(By -+ Jr') < 1.2 X 10U3.

Using a data sample of 1475 000 Z-f q4(y) events collected during 1994 with the L3 detector at LEP, we have studied the purely leptonic decays of heavy flavour mesons, D;

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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