Measurement of radiative tau decays tau -> l gamma nu anti-nu at BaBar

TL;DR

This paper reports precise measurements of tau radiative decay branching fractions using BaBar data, significantly improving the accuracy over previous results for tau -> e gamma nu nu and tau -> mu gamma nu nu decays.

Contribution

First precise measurement of tau radiative decay branching fractions at BaBar, reducing uncertainties compared to prior studies.

Findings

Measured B(tau -> mu gamma nu nu) = (3.69±0.03±0.10)×10^-3

Measured B(tau -> e gamma nu nu) = (1.847±0.015±0.052)×10^-2

Results substantially improve existing measurements.

Abstract

We perform a measurement of the branching fractions for tau -> l gamma nu anti-nu (l= e, mu) decays for a minimum photon energy of 10 MeV in the tau rest frame using 430 fb^-1 of e^+ e^- collisions collected at the center-of-mass energy of the Upsilon(4S) resonance around 10.58GeV with the BaBar detector at the PEP-II storage rings. We find B(tau -> mu gamma nu nu) = (3.69pm0.03pm0.10)x10^-3 and B(tau -> e gamma nu anti-nu) = (1.847pm0.015pm0.052)x10^-2 where the first quoted error is statistical and the second is systematic. These results represent a substantial improvement with respect to existing measurements for both channels.