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

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∓ℓ±Xν, which are generated by a Monte Carlo simulation.