Search for pair produced stable singly charged heavy particles in Z0 decays

A direct search for the exclusive pair production of stable singly charged heavy (SCH) particles in Z0 decays at the LEP e+e− collider is presented. In a scan around the Z0 resonance of 0.4 pb− integrated luminosity, no evidence is seen for the production of slow-moving charged particles as measured by their time-of-flight. We set an upper limit of 1 × 10−3 on the Z0 branching ratio into a pair of SCH fermions in the mass range 29–40 GeV/c2, corresponding to a 3 MeV upper limit on such a contribution to the total width of the Z0. We exclude a fourth generation SCH lepton in the mass range 18.5–42.8 GeV/c2. We also exclude a stable supersymmetric partner of the right-handed lepton, l̃R, in the mass range 21.5–38.8 GeV/c2. All limits are at 95% confidence level.