On spin asymmetry in muon and tau decays

TL;DR

This paper analyzes angular asymmetries in polarized muon and tau decays using the standard model and Michel parameters, highlighting suppressed contributions and estimating second order QED corrections.

Contribution

It provides a detailed examination of spin asymmetries in muon and tau decays, including mass-suppressed effects and QED corrections within a unified framework.

Findings

Mass ratio suppressed contributions are numerically significant.

Second order QED corrections are estimated in the leading logarithm approximation.

The analysis compares standard V-A model with Michel parameterization.

Abstract

The angular asymmetry in decays of polarized muons and tau leptons is discussed. Both the standard $V-A$ Fermi model and the general parameterization via Michel parameters are considered. Numerical importance of contributions suppressed by charged lepton mass ratio is underlined. Contribution of the second order QED correction is estimated in the leading logarithm approximation.