Measurement of the branching fraction of the radiative decay tau(-)->mu(-)(nu)over-bar(mu)nu(tau)gamma

The branching ratio of the radiative tau decay tau(-) --> mu(-) (mu)nu(tau)gamma has been measured using data collected with the OPAL detector at LEP, The result is B(tau(-) --> mu(-) (mu)nu(tau)gamma) = (3.0 +/- 0.4 +/- 0.5) x 10(-3) for photon energies above 20 MeV measured in the tau rest frame. The result is in good agreement with the Standard Model expectation.