A search for neutral Higgs bosons has been performed using the full sample of Z 0 decays collected by the OPAL detector at LEP up to 1995. The data were taken at centre-of-mass energies between 88 GeV and 95 GeV and correspond to an integrated luminosity of approximately 160 pb 1. The present search addresses the processes Z 0 !H 0 Z and h 0 Z , where H 0 is the Higgs boson predicted by the Standard Model and h 0 the lightest neutral scalar Higgs boson predicted in the framework of the Minimal Supersymmetric Standard Model. For the virtual Z 0 boson, Z , the following decay c hannels are considered: Z ! , e + e and +. One candidate event
A search for a supersymmetric partner of the top quark (t 1 ) has been performed by the OPAL experiment i n e + e collisions at LEP. The integrated luminosity of the data sample analysed was 69.1 pb 1 , which corresponds to 1.6810 6 produced Z 0 ! q q e v ents. Not 1 candidates have been found. This study excludes the existence of thet 1 with a mass below 45.1 GeV at 95% C.L., where the mixing angle of left-and right-handed partners is smaller than 0.85 rad or greater than 1.15 rad, and the mass dierence between thet 1 and the lightest neutralino is greater than 5 GeV.
The edge plasma of the ZT-40M [Fusion Technol. 8, 1571 (1985)] reversed-field pinch has been studied using a combination of three different plasma probes: a double-swept Langmuir probe, an electrostatic energy analyzer, and a calorimeter–Langmuir probe. The edge plasma has been measured both with and without a movable graphite tile limiter present nearby in the plasma. Without a limiter a fast nonthermal tail of electrons (T≂350 eV) is detected in the edge plasma with nearly unidirectional flow along B and having a density between 2% and 10% of the cold edge plasma (T≂20 eV). The toroidal sense of this fast electron flow is against the force of the applied electric field. A large power flux along B is measured flowing in the same direction as the fast electrons and is apparently carried by the fast electrons. With the limiter present the fast electrons are still detected in the plasma, but are strongly attenuated in the shadow of the limiter. The measured scrape-off lengths for both the fast electrons and the cold plasma indicate cross-field transport at the rate of, or less than, Bohm diffusion. Estimates indicate that the fast electrons could carry the reversed-field pinch current density at the edge and, from the measured transverse diffusion rates, could also account for the electron energy loss channel in ZT-40 M. The long mean-free-path kinetic nature of these fast electrons suggests that a kinetic process, rather than a magnetohydrodynamic process that is based upon a local Ohm’s law formulation, is responsible for their generation.
We h a v e searched for lepton avour violating Z 0 !e, Z 0 ! e and Z 0 ! decays in a sample of 4:0 10 6 visible Z 0 decays collected with the OPAL detector at LEP during 1991 to 1994. No candidates are found for Z 0 !e. The samples of selected Z 0 !e and Z 0 ! candidates are consistent with the expected background. The following limits are set at 95% condence level:BR(Z 0 ! e) < 1:7 10 6
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