Searches for Lepton Flavor Violation in the Decays tau -> e gamma and tau -> mu gamma

TL;DR

This study conducted comprehensive searches for lepton flavor violation in tau decays to electron or muon plus photon using BaBar data, setting new upper limits on these rare decay processes.

Contribution

It provides the most stringent upper limits to date on the branching fractions of tau to e gamma and tau to mu gamma decays, using the full BaBar dataset.

Findings

No evidence of lepton-flavor-violating decays was observed.

Upper limits on branching fractions were set at 3.3 x 10^-8 for tau -> e gamma.

Upper limits on branching fractions were set at 4.4 x 10^-8 for tau -> mu gamma.

Abstract

Searches for lepton-flavor-violating decay of a tau lepton to a lighter mass lepton and a photon have been performed with the entire dataset of (963 +- 7) x 10^6 tau decays collected by the BaBar detector near the Upsilon(4S), Upsilon(3S) and Upsilon(2S) resonances. The searches yield no evidence of signals and we set upper limits on the branching fractions of BR(tau -> e gamma) < 3.3 x 10^-8 and BR(tau -> mu gamma) < 4.4 x 10^-8 at 90% confidence level.