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 photon propagator, photon-Z0 interference and photonic radiative corrections, these results can be expressed in terms of the lepton neutral current asymmetry parameters: Aτ = 0.1456 ± 0.0076 ± 0.0057, Ae = 0.1454 ± 0.0108 ± 0.0036. These measurements are consistent with the hypothesis of lepton universality and combine to give Aℓ = 0.1455±0.0073. Within the context of the Standard Model this combined result corresponds to = 0.23172± 0.00092. Combing these results with those from the other OPAL neutral current measurements yields a value of = 0.23211 ± 0.00068.
All Science Journal Classification (ASJC) codes
- Engineering (miscellaneous)
- Physics and Astronomy (miscellaneous)