Measurement of the Michel parameters in leptonic tau decays

Abstract

Abstract. The Michel parameters of the leptonic $$\tau$$ decays are measured using the OPAL detector at LEP. The parameters $$\rho_\ell$$, $$\xi_\ell$$, $$(\xi\delta)_\ell$$ (with $$\ell ={\rm e}, \mu$$) and $$\eta_\mu$$ are extracted from the energy spectra of the charged decay leptons and from their energy–energy correlations. A new method involving a global likelihood fit of Monte Carlo generated events with complete detector simulation and background treatment has been applied to the data recorded at center-of-mass energies close to $$\sqrt{s} =m_{\rm Z^0}$$ corresponding to an..