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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%.

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.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.