OBSERVATION OF THE MUONIC DECAY, DS+/--]MU+/-NU-MU

The muonic decay of charmed strange mesons has been observed directly, in the analysis of a sample of 144 decays of charged charmed particles into a muon and no other charged particle. The branching ratio is estimated to be BR(D(s)+/- --> mu+/-nu(mu)) = (4.0(-1.4-0.6)+1.8+0.8+/-1.7) x 10(-3), assuming a ratio r = 0.27 between production cross sections of D(s)+/- and neutral charmed particles. The decay constant f(Ds) is estimated to be (232+/-45+/-20+/-48)MeV/c2 and does not depend on theoretical assumptions.