An Upper Bound on the Decay tau -> mu gamma from Belle

TL;DR

This paper reports a search for the lepton-flavor-violating decay tau -> mu gamma using Belle data, setting a new upper limit on its branching fraction due to no observed signal.

Contribution

The study provides the most stringent upper bound on the tau -> mu gamma decay branching fraction to date.

Findings

No evidence for tau -> mu gamma decay was observed.

An upper limit of 3.1 x 10^{-7} was established for the branching fraction.

The result constrains new physics models predicting lepton flavor violation.

Abstract

We have performed a search for the lepton-flavor-violating decay tau -> mu gamma using a data sample of 86.3fb^{-1} accumulated by the Belle detector at KEK. No evidence for a signal is seen, and we set an upper limit for the branching fraction of B(tau -> mu gamma) < 3.1 x 10^{-7} at the 90% confidence level.