A STUDY OF THE SEMIMUONIC DECAYS OF THE D(S)

We present a study of the Cabibbo-allowed semimuonic decay modes of th e D(S)+ produced in 600 GeV/c pi--emulsion interactions. From a signal of 18.7 +/- 4.9(-0.7)+0.4 events in the D(S)+ --> phimu+nu channel, t he product of production cross section and partial width is measured w ith respect to that for D+ --> K0BAR mu+nu to be (sigma(D(S)+)/sigma( D+)). (GAMMA(D(S)+ --> phimu+nu)GAMMA(D+ --> K0BAR mu+nu)) = 0.56 +/- 0.14 +/- 0.12. The form factor ratios in the decay, obtained by fitti ng to the decay angles and q2, are A2(0)/A1(0) = 2.1(-0.5)+0.6 +/- 0.2 and V(0) = 2.3(-0.9)+1.1 +/- 0.4, where A1(0) and A2(0) are the axial vector form factors and V(0) is the vector form factor, evaluated at q2 = 0. The first observation of D(S)+ --> (etamu+nu + eta'mu+nu) is a lso reported, and GAMMA(D(S)+ --> (etamu+nu + eta'mu+nu))/GAMMA(D(S)--> phimu+nu) is determined to be 3.9 +/- 1.6.