Search for lepton flavour violation in e+e− collisions at –209 GeV

We search for lepton flavour violating events (eμ, eτ and μτ) that could be directly produced in e+e− annihilations, using the full available data sample collected with the OPAL detector at centre-of-mass energies between 189 GeV and 209 GeV. In general, the Standard Model expectations describe the data well for all the channels and at each A single eμ event is observed where according to our Monte Carlo simulations only 0.019 events are expected from Standard Model processes. We obtain the first limits on the cross-sections σ(e+e−→eμ, eτ and μτ) as a function of at LEP2 energies.