Improved tau polarisation measurement.

Using 22 pb of data collected at LEP in 1992 on the peak of the Z resonance, the ALEPH collaboration has measured the polarisation of the tau leptons decaying into $$ev\bar v, \mu v\bar v$$ , πν, ρν and a ν from their individual decay product distributions. The measurement of the tau polarisation as a function of the production polar angle yields the two parameters N and N , where, in terms of the axial and vector couplings g and g , N =2 g g/( g +g). This analysis follows to a large extent the methods devised for the 1990 and 1991 data but with improvements which bring a better understanding of the systematic uncertainties. Combining the 1992 measurements with our previously published results yields N =0.136±0.012±0.009 and N =0.129±0.016±0.005. Assuming e−τ universality, the measurements imply an effective weak mixing angle of sin θ =0.2332±0.0014. [ABSTRACT FROM AUTHOR]