Applicability of perturbative QCD to B->D decays

We examine the applicability of perturbative QCD to B meson decays into D mesons. We find that the perturbative QCD formalism, which includes Sudakov effects at intermediate energy scales, is applicable to the semileptonic decay B --> Dl nu, when the D meson recoils fast. Following this conclusion, we analyze the two-body nonleptonic decays B --> D pi and B --> DDs. By comparing our predictions with experimental data, we extract the matrix element \V-cb\ = 0.044.