A MEASUREMENT OF tau-POLARIZATION AT LEP

Abstract

With a data sample of 86 000 Z --> tau(+)tau>(-)(gamma) events collected in 1990 through 1993 we have measured the polarization of tau-leptons as a function of the production polar angle using the following 1-prong tau decay modes: tau(-) --> e(-)<(nu)over bar>(e) nu(tau),tau(-) --> mu(-)<(nu)over bar>(mu)nu(tau), tau(-) --> pi(-)(K-)nu(tau),tau(-) --> rho(-)nu(tau) and tau(-) --> a(1)(-)nu(tau). We obtain for the ratio of vector to axial-vector weak neutral couplings for electrons gVe/gAe = 0.0791 +/- 0.0099(stat) +/- 0.0025(syst) and taus gV tau/gA tau = 0.0752 +/- 0.0063(stat) +/- 0.0045(syst) consistent with the hypothesis of e - tau universality. Assuming universality of the e - tau neutral current we determine the effective electroweak mixing angle to be sin(2) theta(W)(eff) = 0.2309 +/- 0.0016.