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

Abstract

Four of the Michel parameters and the average tau-neutrino helicity have been measured by analysing tau decay spectra in 147 pb⁻¹ of data collected by the L3 detector. The decays τ⁻ → e⁻ν_τν ̅_e, τ⁻ → μ⁻ν_τν ̅_μ, τ⁻ → π⁻ ν_τ, τ⁻ → ρ⁻ ν_τ , View the MathML source 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.