Perturbative QCD study ofB→D(*)decays

We compute various form factors involved in B→${\mathit{D}}^{\left(\mathrm{*}\right)}$ transitions based on the perturbative QCD formalism, which includes Sudakov effects from the resummation of large radiative corrections in a heavy-light system. A two-parameter model wave function for ${\mathit{D}}^{\left(\mathrm{*}\right)}$ mesons is fixed using data of the nonleptonic decays B→${\mathit{D}}^{\left(\mathrm{*}\right)}$π, from which the ratio of the decay constants ${\mathit{f}}_{\mathit{D}\mathrm{*}}$/${\mathit{f}}_{\mathit{D}}$=0.92 is obtained. We then derive the spectrum of the semileptonic decay B→D*lν in the fast recoil region of the D* meson, and extract the CKM matrix element ‖${\mathit{V}}_{\mathit{cb}}$‖=0.043×(0.12 GeV/${\mathit{f}}_{\mathit{B}}$)×(0.14 GeV/${\mathit{f}}_{\mathit{D}}$), ${\mathit{f}}_{\mathit{B}}$ and ${\mathit{f}}_{\mathit{D}}$ being the B and D meson decay constants, respectively. Here we adopt the convention with the pion decay constant ${\mathit{f}}_{\mathrm{\pi }}$=93 MeV. With these outcomes, we evaluate the decay rate of B→${\mathit{DD}}_{\mathit{s}}$, and estimate the ratio ${\mathit{f}}_{{\mathit{D}}_{\mathit{s}}}$/${\mathit{f}}_{\mathit{D}}$=0.98 from data. Contributions of internal W-emission and W-exchange diagrams are briefly discussed. © 1996 The American Physical Society.