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

TL;DR

This paper reports an updated search for the lepton flavor violating decay tau to mu gamma using CLEO II data, setting a new upper limit on the branching ratio that improves previous constraints.

Contribution

The study provides the most stringent upper limit to date on the branching ratio of tau to mu gamma decay using a complete CLEO II dataset.

Findings

No evidence of tau to mu gamma decay was observed.

The upper limit on the branching ratio is set at 1.0 x 10^{-6} at 90% CL.

The result significantly improves previous experimental limits.

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(\tau \to \mu\gamma) < 1.0 \times 10^{-6} $ at 90% CL, significantly smaller than previous limits. All quoted results are preliminary.