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Bibliographic Details
Main Author: Moussallam, B.
Format: Preprint
Published: 2021
Subjects:
Online Access:https://arxiv.org/abs/2112.04429
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Table of Contents:
  • The rare second-class decay mode of the $τ$ into $ηπν$ could be observed for the first time at Belle II. It is important to try to derive a reliable evaluation of the branching fraction and of the energy distribution of this mode within the standard-model. Many predictions exist already in the literature which can differ by one to two orders of magnitude. Here, an approach based on a systematic use of the property of analyticity of form factors and scattering amplitudes in QCD is discussed. In particular, we will show that the scalar form factor in the $τ$ decay can be related to photon-photon scattering and radiative $ϕ$ decay amplitudes for which precise experimental measurements have been performed by the Belle and KLOE collaborations.