Search for lepton flavour violation in e⁺e⁻ collisions at $\text{s}\text{=189}$–209 GeV

Abstract

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 $\text{s}\text{.}$ 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 $\text{s}$ at LEP2 energies.