A study of the semimuonic decays of the D

We present a study of the Cabibbo-allowed semimuonic decay modes of the DS+ produced in 600 GeV c π − -emulsion interactions. From a signal of 18.7±4.9−0.7+0.4 events in the DS+ → oμ+υ channel, the product of production cross section and partial width is measured with respect to that for D + → K ∗0 μ + υ to be ( σ(D S + ) σ(D + )) . (Λ(D S + → oμ + ν)Λ(D + → K ∗0 μ + ν)) = 0.56 ± 0.14 ± 0.12. The form factor ratios in the decay, obtained by fitting to the decay angles and q2, are A 2 (0) 1 (0) = 2.1 −0.5 +0.6 ± 0.2 and V (0) A 1 (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 DS+ → (ημ+υ + η'μ+υ) is also reported, and Γ (D S + → (ημ + υ + η'μ + υ)) Γ (D S + → oμ + υ) is determined to be 3.9 ± 1.6.