Determination of the Michel parameters and the τ neutrino helicity in τ decay

Abstract

Using the CLEO II detector at the Cornell Electron Storage Ring operated at s√=10.6GeV, we have determined the Michel parameters ρ, ξ, and δ in τ(∓)→l(∓)νν¯ decay as well as the τ neutrino helicity parameter hντ in τ(∓)→π(∓)π(0)ν decay. From a data sample of 3.02×106 produced τ pairs we analyzed events of the topologies e(+)e(-)→τ(+)τ(-)→(l(±)νν¯)(π(∓)π(0)ν) and e(+)e(-)→τ(+)τ(-)→(π(±)π(0)ν¯)(π(∓)π(0)ν). We obtain ρ=0.747ρ=0.747±0.010±0.006, ξ=1.007±0.040±0.015, ξδ=0.745±0.026±0.009, and h(ν)(τ)=-0.995±0.010±0.003, where we have used the previously determined sign of h(ν)(τ) [ARGUS Collaboration, H. Albrecht et al., Z. Phys. C 58, 61 (1993); Phys. Lett. B 349, 576 (1995)]. We also present the Michel parameters as determined from the electron and muon samples separately. All results are in agreement with the standard model V-A interaction.