Search for unstable neutral and charged heavy leptons in e+ e- collisions at s**(1/2) = 130-GeV and 136-GeV

Searches for unstable neutral and charged heavy leptons (L 0 , L ± ) have been performed using a data sample of 2.6 pb −1 at a centre-of-mass energy of s =130 GeV and 2.6 pb −1 at 136 GeV collected with the OPAL detector at LEP during November 1995. No candidate event was observed. If an unstable Dirac neutral heavy lepton L 0 decays only into eW ∗ , μW ∗ or τW ∗ , the lower limits on its mass at 95% C.L. are 62.5 GeV, 63.0 GeV and 57.4 GeV, respectively. The limits are modified for a Majorana L 0 to 51.4 GeV, 52.2 GeV and 44.2 GeV, respectively. For charged heavy leptons, a lower mass limit of 64.5 GeV at 95% C.L. was obtained, if L ± decays into a stable heavy neutrino ν l and W ∗± , and m l ± − m ν l > 10 GeV. If L ± decays through lepton flavour mixing into a massless neutrino ν ℓ and W ∗± , the lower limit on m l ± was determined to be 63.9 GeV at 95% C.L.

electron positron: colliding beams
electron positron: annihilation
heavy lepton: search for
heavy lepton: charged particle
heavy lepton: neutral particle
heavy lepton: pair production
heavy lepton: decay modes
neutrino: Dirac
neutrino: Majorana
heavy lepton: mass

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