Measurement of the τ neutrino helicity and michel parameters in polarized e+e− collisions

We present a new measurement of the τ neutrino helicity hντ and the τ Michel parameters ρ, η, ξ, and the product δξ. The analysis exploits the highly polarized SLC electron beam to extract these quantities directly from a measurement of the τ decay spectra, using the 1993-1995 SLD data sample of 4328 e+e−→Z0 → τ+ τ− events. From the decays τ →πντ and τ →ρντ we obtain a combined value hντ = −0.93±0.10±0.04. The leptonic decay channels yield combined values of ρ=0.72±0.09±0.03, ξ=1.05±0.35±0.04, and δξ=0.88±0.27±0.04.