Nature of theτ−ντ−WCoupling

The electron momentum spectrum observed in the decay $\tau \to {\nu }_{\tau }e{\nu }_e$ is in good agreement with the $V-A$ hypothesis. The measured value of the Michel parameter, $\rho =0.72\mathrm{}\pm 0.15$, excludes a $V+A$ current and disfavors pure $V$ or $A$ currents. The spectrum allows us to set an upper limit of 250 MeV/${\mathit{c}}^2$ (95% confidence level) for the $\tau$ neutrino mass. Finally, by measuring the $\tau$-lifetime upper limit of 2.3×${10}^{-12\mathrm{}}$ sec (95% confidence level), we show that the square of the coupling constant at the $\tau -{\nu }_{\tau }-W$ vertex is at least 12% of full weak strength.