Measurement of the branching ratio for D−s→τ−ν̄τ decays

Abstract Using about 3.9 million hadronic Z decays from e + e − collisions recorded by the OPAL detector at LEP at centre-of-mass energies s ≈M Z , the branching ratio for the decay D − s →τ − ν τ has been measured to be BR ( D − s →τ − ν τ )=(7.0±2.1( stat)±2.0( syst ))%. This result can be used to derive the decay constant of the D − s meson: f D s =(286±44( stat)±41( syst )) MeV .