Measurement of τ decays with the spectrometer ARGUS

Using the ARGUS detector at the e+e- storage ring DORIS II at DESY, we have studied lepton energy spectra in τ decays. We present a ''pseudo-rest-frame'' technique in which the second τ in the event, decaying into a heavy hadronic system, is used as reference. This method allows for the first measurement of the Michel Parameter η in τ decays. We also determine the Michel Parameter ρ in τ→e bar νν decays with a precision comparable to the present world average. The measured values of the parameters ρ=0.735±0.036±0.020 and η=0.03±0.18±0.12 are in good agreement with standard V-A coupling at the τ-ν-W vertex. copyright 1995 American Institute of Physics