Improved tau polarization measurement

ALEPH Collaboration (1995) Improved tau polarization measurement. Zeitschrift für Physik C Particles and Fields, 69 (1). pp. 183-193. ISSN 0170-9739

Abstract

Using 22 pb−1 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 intoevv ¯ ,μvv ¯ ,πν, ρν and a1ν from their individual decay product distributions. The measurement of the tau polarisation as a function of the production polar angle yields the two parametersNτ andNe, where, in terms of the axial and vector couplingsgAl andgVl,Nl=2gVl gAl/(gVl2+gAl2). 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 yieldsNτ=0.136±0.012±0.009 andNe=0.129±0.016±0.005. Assuminge−τ universality, the measurements imply an effective weak mixing angle of sin2θWeff=0.2332±0.0014.