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 a large dataset, resulting in a more stringent upper limit on the branching ratio, with no signal observed.

Contribution

The study provides the most restrictive upper limit to date on the branching ratio of tau to mu gamma decay, improving previous experimental constraints.

Findings

No evidence of tau to mu gamma decay was observed.

The upper limit on the branching ratio is set at 1.1x10^{-6}.

The result significantly improves previous limits.

Abstract

We present an update of the search for the lepton family number violating decay tau -> mu gamma using 12.6 million tau+tau- pairs collected with the CLEO detector. No evidence of a signal has been found and the corresponding upper limit is BR(tau -> mu gamma) < 1.1x10^{-6} at 90% CL, significantly smaller than previous experimental limits.