A measurement of the τ- → μ- (ν)over-barμντ branching ratio

The tau(-) --> mu(-)(nu) over bar (mu)nu(tau) branching ratio has been measured using data collected from 1990 to 1995 by the OPAL detector at the LEP collider. The resulting value of B (tau(-) --> mu-(nu) over bar (mu)nu(tau))= 0. 1734 +/- 0.0009(stat) +/- 0.0006(syst) has been used in conjunction with other OPAL measurements to test lepton universality, yielding the coupling constant ratios g(mu)/g(e) = 1.0005 +/- 0.0044 and g(tau)/g(e) = 1.0031 +/- 0.0048, in good agreement with the Standard Model prediction of unity. A value for the Michel parameter eta = 0.004 +/- 0.037 has also been determined and used to find a limit for the mass of the charged Higgs boson, m(H)+/- > 1.28 tan beta, in the Minimal Supersymmetric Standard Model. (C) 2002 Elsevier Science B.V. All rights reserved.