Update of the Search for the Neutrinoless Decay $\tau \to \mu \gamma$

Abstract

We present an update of the search for the lepton family number violating decay $\tau \to \mu \gamma$ using a complete CLEO II data sample of 12.6 million ${\tau }^{+}{\tau }^{-}$ pairs. No evidence of a signal has been found and the corresponding upper limit is $ \BR(τ\to μγ) < 1.0 \times 10^{-6} $ at 90% CL, significantly smaller than previous limits. All quoted results are preliminary.

9 pages postscript, also available through http://w4.lns.cornell.edu/public/CLNS