Radiative τ leptonic decays and the possibility to determine the τ dipole moments

Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, University of Bern, CH-3012 Bern, Switzerland

^a e-mail: fael@itp.unibe.ch

Published online: 26 April 2016

Abstract

Precise data on radiative leptonic τ decays offer the opportunity to probe the electromagnetic properties of the τ and may allow to determine its anomalous magnetic moment which, in spite of its precise Standard Model prediction, has never been measured. Recently, the branching fractions of the radiative leptonic τ decays ($\tau \to l\nu \overline{\nu }\gamma$, with l = e, μ) were measured by the Babar collaboration. These precise measurements, with a relative error of about 3%, must be compared with the branching ratios at the next-to-leading order in QED. Indeed the radiative corrections are expected to be of order 10%, for l = e, and 3%, for l = μ. Here, we present the prediction of the differential decay rates and branching ratios of the radiative leptonic τ decays in the Standard Model at the next-to-leading order and we compare them with the recent Babar measurements. Moreover, we report on a dedicated feasibility study for the measurements of the τ anomalous magnetic moment at Belle and Belle II.