A search for lepton flavour violation in Z0 decays

We have searched for lepton flavour violation in about 14000 Z0 decays into collinear lepton pairs, recorded in an energy scan around the Z0 resonance. Decays of the type Z0→eτ, Z0→μτ and Z0→eμ have been considered. Observed candidates in the eτ and μτ modes are consistent with expected Z0→τ+τ− backgrounds; no candidates are observed for the eμ mode. We obtain limits (at 95% confidence level) on the branching ratios for such Z0 decays of 7.2×10−5 for the eτ decay, 35×10−5 for the μτ decay and 4.6×10−5 for the eμ decay.