We report on a measurement of the branching fractions for $B^{-}\to D^{(*)+}{\pi }^{-}{\ell }^{-}{\overline{\nu }}_{\ell }$ and $\overline{B^0}\to D^{(*)0}{\pi }^{+}{\ell }^{-}{\overline{\nu }}_{\ell }$ with $275\times {10}^6$ $B\overline{B}$ events collected at the ${\rm Y}(4S)$ resonance with the Belle detector at KEKB. Events are tagged by fully reconstructing one of the $B$ mesons in hadronic modes. We obtain $\mathcal{B}(B^{-}\to D^{+}{\pi }^{-}{\ell }^{-}{\overline{\nu }}_{\ell })=(0.54\pm 0.07(\mathrm{stat})\pm 0.07(\mathrm{syst})\pm 0.06(\mathrm{BR}))\times {10}^{-2}$, $\mathcal{B}(B^{-}\to D^{*+}{\pi }^{-}{\ell }^{-}{\overline{\nu }}_{\ell })=(0.67\pm 0.11(\mathrm{stat})\pm 0.09(\mathrm{syst})\pm 0.03(\mathrm{BR}))\times {10}^{-2}$, $\mathcal{B}(\overline{B^0}\to D^0{\pi }^{+}{\ell }^{-}{\overline{\nu }}_{\ell })=(0.33\pm 0.06(\mathrm{stat})\pm 0.06(\mathrm{syst})\pm 0.03(\mathrm{BR}))\times {10}^{-2}$, $\mathcal{B}(\overline{B^0}\to D^{*0}{\pi }^{+}{\ell }^{-}{\overline{\nu }}_{\ell })=(0.65\pm 0.12(\mathrm{stat})\pm 0.08(\mathrm{syst})\pm 0.05(\mathrm{BR}))\times {10}^{-2}$, where the third error comes from the error on $\overline{B}\to D^{(*)}{\ell }^{-}{\overline{\nu }}_{\ell }$ decays. Contributions from $\overline{B^0}\to D^{*+}{\ell }^{-}{\overline{\nu }}_{\ell }$ decays are excluded in the measurement of $\overline{B^0}\to D^0{\pi }^{+}{\ell }^{-}{\overline{\nu }}_{\ell }$.

• Received 16 August 2005

DOI:https://doi.org/10.1103/PhysRevD.72.051109