Observation of Radiative Leptonic Decay of the Tau Lepton

TL;DR

This study measures the branching fractions of radiative tau decays to muons and electrons, confirming consistency with Standard Model predictions using data from the CLEO II detector.

Contribution

First precise measurement of radiative tau decay branching fractions at a 10 MeV photon energy threshold, validating Standard Model predictions.

Findings

Branching fraction for tau -> mu nu nu gamma: (3.61+-0.16+-0.35)*10^{-3}

Branching fraction for tau -> e nu nu gamma: (1.75+-0.06+-0.17)*10^{-2}

Results agree with Standard Model expectations.

Abstract

Using 4.68 fb^{-1} of e^+e^- annihilation data collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR) we have studied tau radiative decays tau -> mu nu nu gamma and tau -> e nu nu gamma. For a 10 MeV minimum photon energy in the tau rest frame, the branching fraction of radiative tau decay to a muon or electron is measured to be (3.61+-0.16+-0.35)*10^{-3} or (1.75+-0.06+-0.17)*10^{-2}, respectively. The branching fractions are in agreement with the Standard Model theoretical predictions.