Search for Lepton Flavour Violation in e+e- Collisions at sqrt(s) = 189 - 209 GeV

TL;DR

This paper reports a search for lepton flavour violation in electron-positron collisions at energies between 189 and 209 GeV, finding no significant deviations from the Standard Model and setting new cross-section limits.

Contribution

First limits on lepton flavour violating processes in e+e- collisions at LEP2 energies are established using the full OPAL data sample.

Findings

Standard Model describes data well across channels

One e mu event observed against 0.019 expected

New upper limits set on cross-sections for LFV processes

Abstract

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 sqrt(s). A single e mu 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 sqrt(s) at LEP2 energies.