Observation of Tree-Level B Decays with ss¯ 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 ss̅ pair. We present observations of the decays B-→Ds(*)+K-π- and B̅ 0→Ds+KS0π- and evidence for B-→Ds+K-K- and set upper limits on the branching fractions for B̅ 0→Ds*+KS0π- and B-→Ds*+K-K- using 383×106 Υ(4S)→BB̅ events collected by the BABAR detector at SLAC. We present evidence that the invariant mass distributions of Ds(*)+K- pairs from B-→Ds(*)+K-π- decays are inconsistent with the phase-space model, suggesting the presence of charm resonances lying below the Ds(*)+K- threshold.