Search for the lepton flavour violating decay $\tau^-\to \mu^-\mu^+\mu^-$

TL;DR

This paper reports a search for the lepton flavor violating decay of tau into three muons using LHCb data, setting a new upper limit on its branching fraction due to no observed signal.

Contribution

It provides the first search for $ au^- o \mu^-\mu^+\mu^-$ decay at LHCb and establishes a new upper limit on its branching fraction.

Findings

No evidence for the decay was observed.

A new upper limit on the branching fraction was set at 4.6 x 10^-8.

The analysis used 3.0 fb^-1 of data from 7 and 8 TeV collisions.

Abstract

A search for the lepton flavour violating decay $\tau^-\to \mu^-\mu^+\mu^-$ is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of $1.0\mathrm{\,fb}^{-1}$ of proton-proton collisions at a centre-of-mass energy of $7\mathrm{\,Te\kern -0.1em V}$ and $2.0\mathrm{\,fb}^{-1}$ at $8\mathrm{\,Te\kern -0.1em V}$. No evidence is found for a signal, and a limit is set at $90\%$ confidence level on the branching fraction, $\mathcal{B}(\tau^-\to \mu^-\mu^+\mu^-) < 4.6 \times 10^{-8}$.