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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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

.5 ® /0 3 7 0 -2 6 9 3 ( 94) 004 8 7 -R 224 L3 Callaboration / Physics Letters B 328 (1994) We present a study of the inclusive production of 7r°, 77, and A based on 929,000 hadronic Z decays recorded with the L3 detector at LEP. The measured inclusive momentum distributions have been compared with predictions from parton shower models as well as an analytical Quantum Chromodynamics calculation. Comparing to low energy e+e " data, we find that Q CD describes the energy evolution o f the hadron spectrum.

Tests of QED at LEP energies using \(e^{+}e^{-}\rightarrow \gamma\gamma (\gamma)\) and \(e^{+}e^{-}\rightarrow \l^{+}l^{-}\gamma\gamma\) M. Acciarri (et al) Citation for published version (APA):M. Acciarri (et al), M., Bobbink, G. J., Bouwens, B., Duinker, P., Erné, F. C., Koffeman, E. N., ... Ijzerman, M. P. (1995). Tests of QED at LEP energies using \(e^{+}e^{-}\rightarrow \gamma\gamma (\gamma)\) and \(e^{+}e^{-}\rightarrow \l^{+}l^{-}\gamma\gamma\). Physics Letters B, 353, 136. DOI: 10.1016/0370-269300527-R General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. PHYSICS LETTERS B EJLSEVIERPhysics Letters B 353 (1995) 136-144 Tests of QED at LEP energies using e+e--+ yy (--y) and e+e-+ l+l-yy AbstractTotal and differential cross sections for the process e+e-+ yy( y) , and the total cross section for the process efe-+ yyy, are measured at energies around 91 GeV using the data collected with the L3 detector f?om 1991 to 1993. We set lower limits, at 95% CL, on a contact interaction energy scale parameter A > 602 GeV, on the mass of an excited electron m,* >146 GeV and on the QED cut-off parameters A+ > 149 GeV and A-> 143 GeV. Upper limits are also set on the branching fractions of Z decaying into yy, #y and rly of 5.2 x 10m5, 5.2 x lo-' and 7.6 x lo-' respectively. The reactions e+e-A e+e-ny (e = e, ,u, Q-) are studied using the data collected from 1990 to 1994. The data are consistent with the QED expectations.