Analysis of the Decay Tauon Going to Rho Particle Neutrino

An analysis of the decay tau^ {+/-}torho^{+/- }nu_{tau} has been undertaken in the OPAL experiment at CERN, in Geneva, Switzerland. From the 1990 experimental run of the LEP particle accelerator, a sample of 3310 e^+ e^-totau^+tau ^- events was selected, with an estimated contamination of 1.9%. Requirements were applied to select a subsample of tau^{+/- }torho^{+/-}nu _tau decays, resulting in 650 decays being found. From studies with simulated data, the non -rho contamination in this sample was estimated to be approximately 22%, and the rho selection efficiency to be approximately 33%. The Branching fraction for the decay is measured to be B(tau^{+/-}to rho^{+/-}nu_{ tau}) = 0.234+/- 0.009(stat.) +/- _sp{0.009}{0.010} (syst.). The mean tau polarisation at the peak of the Z^0 resonance is measured to be P_tau= -0.17+/- 0.10(stat.) +/- 0.08(syst.). From the tau polarisation we extract a measurement of the electroweak mixing sin^2 theta_{W}=0.225 +/- 0.015. The tau polarisation asymmetry at the peak of the Z^0 resonance is also measured, A_sp{FB }{Pol}=-0.09+/- 0.13+/- 0.05. From the polarisation measurement, v_tau /a_tau=0.09+/- 0.06, and from the polarisation asymmetry v_{e }/a_{e}=0.06+/- 0.10. Combined with previous LEP measurements of the tau polarisation, the electroweak mixing is found to be sin^2 theta_{W}=0.2308+/- 0.0042. Combined with measurements from other experiments, one obtains sin ^2 theta_{W }=0.2303+/- 0.0013.