Measurement of the Michel parameters and the average tau-neutrino helicity from tau decays at LEP

Four of the Michel parameters and the average tau-neutrino helicity have been measured by analysing tau decay spectra in 147 pb−1of data collected by the L3 detector. The decays τ−→e−ντν̄e, τ−→μ−ντν̄μ, τ−→π−ντ, τ−→ρ−ντ and their charge conjugates were considered. The results: ρ=0.762±0.035, η=0.27±0.14, ξ=0.70±0.16, ξδ=0.70±0.11 and ξh=−1.032±0.031 are consistent with a V−A structure for the weak charged current and lepton universality.