Applicability of perturbative QCD toB→Ddecays

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→Dlν, when the D meson recoils fast. Following this conclusion, we analyze the two-body nonleptonic decays B→Dπ and B→${\mathit{DD}}_{\mathit{s}}$. By comparing our predictions with experimental data, we extract the matrix element ‖${\mathit{V}}_{\mathit{c}\mathit{b}}$‖=0.044.