A STUDY OF THE DECAYS OF TAU LEPTONS PRODUCED ON THE Z-RESONANCE AT LEP

From the analysis of a data sample corresponding to an integrated luminosity of 4.63 pb-1 taken during the 1990 run of LEP at centre of mass energies between 88.2 GeV an 94.2 GeV, the tau decays {Mathematical expression} and their charge conjugates have been studied. The following branching ratios have been measured; {Mathematical expression}, {Mathematical expression}, Br(τ- → π- (K-)vτ)=11.9±0.7±0.7%, BR (τ- → ρ- vτ)= 22.4±0.8±1.3%, in good agreement with world averages. The measured electronic and muonic branching ratios lead to a measurement of the strong coupling constant, αs (mτ) = 0.26-0.12 +0.09. Extrapolating the αs value from mτ to mZ yields αs (mZ) = 0.109-0.028 +0.012. The average polarization Pτ of taus produced in Z → τs τs decays has also been measured using the above decay modes. The weighted mean of the polarizations obtained from the four decay modes is Pτ=-0.24±0.07. This value of Pτ gives, in the improved Born approximation, a ratio between the axial and vector coupling constants of the tau of υτ/aτ = 0.12 ± 0.04, and hence a value of the effective electroweak mixing parameter sin2 θW(mZ 2). © 1992 Springer-Verlag.
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