Search for lepton flavour violation in e+e- collisions at √s=189-209 GeV

We search for lepton flavour violating events (e mu, e tau and mu tau) 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 roots. A single ett 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 sigma (e(+)e(-) --> e mu, e tau and mu tau) as a function of roots at LEP2 energies. (C) 2001 Elsevier Science B.V. All rights reserved.