MEASURING NU(TAU)-MASS FROM TAU-BRANCHING FRACTIONS

We have derived constraints on the tan neutrino mass and fourth genera tion mixing from an analysis of the tan lifetime and the partial width s of tan lepton decays : tau(-) --> e(-)<(nu)over bar>(e) nu(tau), tau (-) --> mu(-)<(nu)over bar>(mu)nu(tau), tau --> pi(-)nu(tau), and tau --> K(-)nu(tau). We present predictions for the tau decay widths, allo wing for a non-zero tau neutrino mass, m(nu tau), and for mixing with a neutrino of mass m(nu L) > M-Z/2, which is parametrised using a Cabi bbo-like mixing angle, theta(L). By comparison of these theoretical pr edictions with the experimental measurements, we obtain the following bounds at the 90% confidence level: m(nu tau) < 42 MeV and sin(2) thet a(L) < 0.014.