Paper detail

Study of Michel parameters in leptonic $τ$ decays at Belle

We present a study of Michel parameters in leptonic $τ$ decays using experimental information collected at the Belle detector. Michel parameters are extracted in the unbinned maximum likelihood fit of the $(τ^\mp\to\ell^\mpνν,τ^\pm\toπ^\pmπ^0ν)$ events in the full nine-dimensional phase space. We exploit the spin-spin correlation of tau leptons to extract $ξ_ρξ$ and $ξ_ρξδ$ in addition to the $ρ$ and $η$ parameters.