We report observations of the Cabibbo suppressed decays B-->D((*))K- using a 10.4 fb(-1) data sample accumulated at the Upsilon(4S) resonance with the Belle detector at the KEKB e(+)e(-) storage ring. We find that the ratios of Cabibbo suppressed to Cabibbo favored branching fractions are B(B--->D0K-)/B(B--->D0pi(-)) = 0.079+/-0.009+/-0.006, B(B(0)-->D+K-)/B(B(0)-->D+pi(-)) = 0.068+/-0.015+/-0.007, B(B--->D(*0)K-)/B(B--->D(*0)pi(-)) = 0.078+/-0.019+/-0.009, and B(B(0)-->D(*+)K-)/B(B(0)-->D(*+)pi(-)) = 0.074+/-0.015+/-0.006. These are the first observations of the B-->D+K-, D(*0)K-, and D(*+)K- decay processes.

We report the observation of a narrow charmoniumlike state produced in the exclusive decay process B+/--->K+/-pi(+)pi(-)J/psi. This state, which decays into pi(+)pi(-)J/psi, has a mass of 3872.0+/-0.6(stat)+/-0.5(syst) MeV, a value that is very near the M(D0)+M(D(*0)) mass threshold. The results are based on an analysis of 152M B-Bmacr; events collected at the Upsilon(4S) resonance in the Belle detector at the KEKB collider. The signal has a statistical significance that is in excess of 10sigma.

We report a measurement of the branching fraction ratios R(D ( * ) ) ofB → D ( * ) τ −ν τ relative tō B → D ( * ) −ν (where = e or µ) using the full Belle data sample of 772 × 10 6 BB pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. The measured values are R(D) = 0.375 ± 0.064(stat.) ± 0.026(syst.) and R(D * ) = 0.293 ± 0.038(stat.) ± 0.015(syst.). The analysis uses hadronic reconstruction of the tag-side B meson and purely leptonic τ decays. The results are consistent with earlier measurements and do not show a significant deviation from the standard model prediction.