Search for Lepton-Flavor Violation in the Decay $\tau^-\to\ell^-\ell^+\ell^-$

TL;DR

This study searched for lepton-flavor-violating tau decays into three leptons using BaBar data, finding no evidence and setting upper limits on branching fractions between 1 and 3 times 10^{-7}.

Contribution

First search for tau to three lepton decays at BaBar, establishing new upper limits on branching fractions for these rare processes.

Findings

No significant excess of events observed.

Upper limits on branching fractions range from (1-3)×10^{-7}.

Results constrain models predicting lepton-flavor violation.

Abstract

A search for the lepton-flavor-violating decay of the tau into three charged leptons has been performed using $91.5 \mathrm{fb}^{-1}$ of data collected at an $e^+e^-$ center-of-mass energy of 10.58 GeV with the BaBar detector at the PEP-II storage ring. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range $(1-3) \times 10^{-7}$ at 90% confidence level.