Production ofD S + mesons inB decays and determination of $$f_{D_S } $$

The production ofD S + mesons inB meson decays, and inq\(\bar q\) continuum events, has been studied with the ARGUS detector at thee+e− storage ring DORIS II. In addition to the measurement of inclusiveD S + production in γ(4S)→B\(\bar B\) decays, all eight two-body decay modesB→D S (*) D(*) have been measured with branching ratios between 1% and 3%. By comparing our inclusive and exclusive results to predictions of heavy quark effective theory, a value of (267±28) MeV × [2.7%/BR(D s + →φπ+)]1/2 is obtained for the weak decay constant fD S (*) , averaged overD S + andD S *+ mesons.