Correlation measurements in Z→τ τ- and the τ neutrino helicity

Abstract

Using data collected with the ALEPH detector at LEP correlations between the decay products of the τ+ and τ- produced in the decay of the Z have been measured. The measurements performed in the decays τ→πν and τ→ρ{variant}ν place limits on deviations from the Standard Model. These are given by the parameter ζ with ζ = -1 for the Standard Model. The measured values are ζπ = -0.95 ± 0.11 ± 0.05 and ζρ{variant} = -1.03 ± 0.11 ± 0.05. For models which predict ζπ = ζρ{variant} = ζ - interpreted as the average τ neutrino helicity - the measurement is ζ = -0.99 ± 0.07 ± 0.04. © 1994.