D. Buskulic et al., MICHEL PARAMETERS AND TAU-NEUTRINO HELICITY FROM DECAY CORRELATIONS IN Z-]TAU(-)()TAU(), Physics letters. Section B, 346(3-4), 1995, pp. 379-388
The Michel parameters and the average tau-neutrino helicity are measur
ed using correlations between the decays of the tau(+) and tau(-) prod
uced on the Z resonance and observed in the ALEPH detector at LEP. The
Michel parameters, rho(e), eta(e), xi(e), (delta xi)(e), are determin
ed from tau --> e ($) over bar upsilon(e) upsilon(tau) with e = (e, mu
), and the average tau neutrino helicity, (h(upsilon(tau))), from tau
--> h tau with h = (pi, rho, a(1)). The results obtained with e-mu uni
versality are: rho(e) = 0.751 +/- 0.039 +/- 0.022, eta(e) = -0.04 +/-
0.15 +/- 0.11, xi(e) = 1.18 +/- 0.15 +/- 0.06, (delta xi)(e) = 0.88 +/
- 0.11 +/- 0.07, and the average tau neutrino helicity (h(upsilon(tau)
)) = -1.006 +/- 0.032 +/- 0.019. No significant deviation from the Sta
ndard Model V-A prediction is observed.