Precision neutral current asymmetry parameter measurements from the Tau polarization at LEP

Abstract

Measurements of the τ lepton polarization and forward-backward polarization asymmetry near the Z0 resonance using the OPAL detector are described. The measurements are based on analyses of τ → eνeντ, τ → μνμντ, τ → πντ, τ → ρντ, and τ → a1ντ decays from a sample of 144,810 e+e- → τ+τ- candidates corresponding to an integrated luminosity of 151 pb-1. Assuming that the τ lepton decays according to V-A theory, we measure the average τ polarization near √s = Mz to be 〈Pτ〉 = (-14.10 ± 0.73 ± 0.55)% and the τ polarization forward-backward asymmetry to be AFBpol = (-10.55 ± 0.76 ± 0.25)%, where the first error is statistical and the second systematic. Taking into account the small effects of the ph..