A new method for the measurement of the Michel parameters that describe the daughter muon polarization in the τ−→ μ−ν¯μντ decay

Abstract

This paper provides a detailed description of the method for the first direct measurement of all Michel parameters in the τ⁻→ μ⁻$\overline{\nu }$_μν_τ decay related to the polarization of the daughter muon. An application of the suggested method in the existing and future experiments at e⁺e⁻ colliders is considered. We have performed a feasibility study for the future Super Charm-Tau Factory and Belle II experiments. For the first one, the sensitivity to the Michel parameters ξ′, ξ′′, η′′, α′/A, and β′/A is estimated. For the latter, only one Michel parameter, ξ′, for which the sensitivity is maximum, is considered.