Observation of Tree-Level B Decays with ss[over ¯] Production from Gluon Radiation

We report on our search for decays proceeding via a tree-level b -> c quark transition in which a gluon radiates into an s (s) over bar pair. We present observations of the decays B--> D-s(*)K-+(-) pi(-) and (B) over bar (0) -> (Ds+KS0)pi(-) and evidence for B--> D-s(+) K- K- and set upper limits on the branching fractions for (B) over bar (0) -> (Ds*+KS0) pi(-) and B- -> Ds*+K- K- using 383 x 10(6) gamma(4S)-> B (B) over bar events collected by the BABAR detector at SLAC. We present evidence that the invariant mass distributions of Ds(*)+K- pairs from B- -> D-s(*)K-+(-)pi(-) decays are inconsistent with the phase-space model, suggesting the presence of charm resonances lying below the D-s(*)(+) K- threshold.