Measurement of the branching fraction of $B\to D^{(\ast )}\pi \ell \nu$ at Belle using hadronic tagging in fully reconstructed events

Abstract

We report a measurement of the branching fraction of the decay $B\to D^{(\ast )}\pi \ell \nu$. The analysis uses 772$\times 10^6$ $B\bar{B}$ pairs produced in $e^{+}{e}^{-}\to {\rm Y}(4S)$ 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 $B\to D^{(\ast )}\pi \ell \nu$ $(\ell =e,\mu )$. The measured branching fractions are $\mathcal{B}(B^{+}\to D^{-}{\pi }^{+}{\ell }^{+}\nu )$ = [4.55 $\pm$ 0.27 (stat.) $\pm$ 0.39 (syst.)]$\times 10^{-3}$, $\mathcal{B}(B^0\to {\bar{D}}^0{\pi }^{-}{\ell }^{+}\nu )$ = [4.05 $\pm$ 0.36 (stat.) $\pm$ 0.41 (syst.)]$\times 10^{-3}$, $\mathcal{B}(B^{+}\to D^{\ast -}{\pi }^{+}{\ell }^{+}\nu )$ = [6.03 $\pm$ 0.43 (stat.) $\pm$ 0.38 (syst.)]$\times 10^{-3}$, and $\mathcal{B}(B^0\to {\bar{D}}^{\ast 0}{\pi }^{-}{\ell }^{+}\nu )$ = [6.46 $\pm$ 0.53 (stat.) $\pm$ 0.52 (syst.)]$\times 10^{-3}$. These are in good agreement with the current world average values.

arXiv comment8 pages, 2 figures, submitted to PRD

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