Search for Lepton Flavour Violation in the Decay τ±→μ±γ

A search for the lepton flavour violating decay τ ± → μ ± γ has been performed using 221.4 fb−1 of data collected at an e+e− centre-of-mass energy of 10.58 GeV with the BaBar detector at the PEP-II storage ring. The search has an efficiency of (7.45 ± 0.65)% for an expected background level of 6.2 ± 0.5 events. In the final sample 4 candidate events are selected. As there is no evidence for a signal in this data, for this preliminary result we set an upper limit of B ( τ ± → μ ± γ ) 9 × 10 −8 at 90% CL using the method of Feldman and Cousins.