Correlated decay widths of a τ pair for the Michel parameter measurement

We express the correlated decay widths of a τ-τ+ pair produced by an e-e+ collision in terms of the observed variables in order to measure the Michel parameters. The decay widths are derived from theoretical predictions by integrating over the unobserved τ direction. The introduction of a coordinate system for the τ direction makes it easy to formulate the integral. Based on the new formulation, we extract the Michel parameters from typical leptonic decays, τ-τ+→l-+ρ±Xν and τ-τ+→l-+±Xν, which are generated by a Monte Carlo simulation