Measurement of the branching fraction of $B \rightarrow D^{(*)}π\ellν$ at Belle using hadronic tagging in fully reconstructed events
We report a measurement of the branching fraction of the decay $B \rightarrow D^{(*)}π\ellν$. The analysis uses 772$\times 10^6$ $B\bar{B}$ pairs produced in $e^+e^-\rightarrow Υ(4S)$ data recorded by the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider. The tagging $B$ meson in the decay is fully reconstructed in a hadronic decay mode. On the signal side, we reconstruct the decay $B \rightarrow D^{(*)}π\ellν$ $(\ell=e,μ)$. The measured branching fractions are $\mathcal{B}(B^+ \rightarrow D^-π^+ \ell^+ν)$ = [4.55 $\pm$ 0.27 (stat.) $\pm$ 0.39 (syst.)]$\times 10^{-3}$, $\mathcal{B}(B^0 \rightarrow \bar{D}^0π^- \ell^+ν)$ = [4.05 $\pm$ 0.36 (stat.) $\pm$ 0.41 (syst.)]$\times 10^{-3}$, $\mathcal{B}(B^+ \rightarrow D^{*-}π^+ \ell^+ν)$ = [6.03 $\pm$ 0.43 (stat.) $\pm$ 0.38 (syst.)]$\times 10^{-3}$, and $\mathcal{B}(B^0 \rightarrow \bar{D}^{*0}π^- \ell^+ν)$ = [6.46 $\pm$ 0.53 (stat.) $\pm$ 0.52 (syst.)]$\times 10^{-3}$. These are in good agreement with the current world average values.