Search for the Lepton-Flavor-Violating Decay $\tau^- \to \mu^- \eta$ at Belle

TL;DR

This study searched for a rare lepton-flavor-violating decay of tau leptons into muons and eta mesons using Belle detector data, setting a new upper limit on its branching fraction.

Contribution

First search for the decay $ au^- o ^- $ at Belle, providing the most stringent upper limit to date.

Findings

No signal candidates observed.

Upper limit on branching fraction: < 3.4 x 10^{-7}.

Data sample of 84.3 fb^{-1} used.

Abstract

We have searched for the Lepton Flavor Violating decay $\tau^- \to \mu^- \eta$ using a data sample of 84.3 fb$^{-1}$ accumulated with the Belle detector at KEK. The $\eta$-meson was detected through the decay modes: $\eta \to \gamma\gamma$ and $\pi^+\pi^-\pi^0$. No signal candidates are found, and we obtain an upper limit for the branching fraction ${\cal B}(\tau^- \to \mu^- \eta)<3.4\times 10^{-7}$ at the 90% confidence level.