A measurement of τ polarization at LEP

Abstract

With a data sample of 86 000 Z → τ + τ − (γ) events collected in 1990 through 1993 we have measured the polarization of τ-leptons as a function of the production polar angle using the following 1-prong τ decay modes: τ − → e − v e v τ , τ − →π − (K − )v τ , τ − →ϱ − v τ and τ − →a 1 − v τ . We obtain for the ratio vector to axial-vector weak neutral couplings for electrons g Ve / g Ae =0.0791±0.0099(stat)±0.0025 (syst) and taus g Vτ / g Aτ =0.0752±0.0063 (stat)±0.0045 (syst) consistent with the hypothesis of e - τ universality. Assuming universality of the e - τ neutral current we determine the effective electroweak mixing angle to be sin 2 θ eff w = 0.2309 ± 0.0016.