A precise measurement of the tau polarization and its forward-backward asymmetry at LEP

Abstract

A measurement of the τ lepton polarization and its forward-backward asymmetry at the Z0 resonance using the OPAL detector is described. The measurement is based on analyses of τ→ρντ, τ→π(K)ντ, τ→eν̄eντ, τ→μν̄μντ, and τ→a1ντ decays from a sample of 89075 e+e-→τ+τ- candidates corresponding to an integrated luminosity of 117 pb-1. Assuming that the τ lepton decays according to V-A theory, we measure the average τ polarization at √s=MZ to be 〈Pτ〉 = (-13.0 ± 0.9 ± 0.9)% and the τ polarization forward-backward asymmetry to be Apol FB = (-9.4 ±1.0±0.4)%, where the first error is statistical and the second systematic. These results are consistent with the hypothesis of lepton universality and, when ..