# Measurement of the Michel parameters and the $\nu_{\tau}$ helicity in $\tau$ lepton decays

Abstract : A measurement of the Michel parameters and the average $\nu_\tau$ helicity in $\tau$ lepton decays is described. The data was collected with the ALEPH detector at LEP during the years 1991 to 1995. A total integrated luminosity of 155\,$\text{pb}^{-1}$ is analysed. The Michel parameters $\rho_l$, $\xi_l$, $(\xi\delta)_l$ ($l=e,\mu$), and $\eta_\mu$ are determined for the leptonic deca ys, and the chirality parameters $\xi_\pi$, $\xi_\rho$, and $\xi_{a_1}$ for the hadronic final states. Under the assumptions of $e$\bis $\mu$ universality and $\xi_\pi=\xi_\rho=\xi_{a_1}$, the values $\rho_l=0.742\pm 0.016, \eta_l=0.01 2\pm 0.026,\break (\xi\delta)_l=0.776\pm 0.051, \xi_l=0.986\pm 0.074$, and $\xi_h=0.992\pm 0.011$ are obtained. No significant deviation is observed from the Standard Model assumption of the \ vma{} structure of the charged weak interaction.
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Journal articles

Cited literature [26 references]

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Submitted on : Thursday, January 17, 2002 - 10:28:51 AM
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### Identifiers

• HAL Id : in2p3-00010979, version 1

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### Citation

A. Heister, S. Schael, R. Barate, I. de Bonis, D. Decamp, et al.. Measurement of the Michel parameters and the $\nu_{\tau}$ helicity in $\tau$ lepton decays. European Physical Journal C: Particles and Fields, Springer Verlag (Germany), 2001, 22, pp.217-230. ⟨in2p3-00010979⟩

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