EPJ

2023 Impact factor 4.2
EPJ C - Particles and Fields
Particles and Fields

Eur. Phys. J. C 16, 229-252
DOI 10.1007/s100520000402

A study of the Lorentz structure in tau decays

The DELPHI Collaboration

P.Abreu22 et al.

22 LIP, IST, FCUL - Av. Elias Garcia, 14-1o, 1000 Lisboa Codex, Portugal

Received: 14 February 2000 / Revised version: 7 March 2000 /
Published online: 8 May 2000 - © Springer-Verlag 2000

Abstract
This paper describes a measurement of the Michel parameters, $\eta$, $\rho$, $\xi$, $\xi \delta$, and the average $\nu_{\tau}$helicity, $h_{\nu_{\tau}}$, in $\tau$ lepton decays together with the first measurement of the tensor coupling in the weak charged current. The $\tau^{+} \tau^{-}$ pairs were produced at the LEP e+ e-collider at CERN from 1992 through 1995 in the DELPHI detector. Assuming lepton universality in the decays of the $\tau$ the measured values of the parameters were: $\eta = -0.005 \pm 0.036 \pm 0.037$, $\rho = 0.775 \pm 0.023 \pm 0.020$, $\xi = 0.929 \pm 0.070 \pm 0.030$, $\xi\delta = 0.779 \pm 0.070 \pm 0.028$, $h_{\nu_{\tau}} = -0.997 \pm 0.027 \pm 0.011$. The strength of the tensor coupling was measured to be $\kappa^W_\tau = -0.029 \pm 0.036 \pm 0.018$. The first error is statistical and the second error is systematic in all cases. The results are consistent with the $V\!-\!A$ structure of the weak charged current in decays of the $\tau$ lepton.

Copyright Società Italiana di Fisica, Springer-Verlag 2000

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