Measurement of the Branching Fractions of $\overline{B}\to D^{**}{\ell }^{-}{\overline{\nu }}_{\ell }$ Decays in Events Tagged by a Fully Reconstructed $B$ Meson

We report a measurement of the branching fractions of $\overline{B}\to D^{**}{\ell }^{-}{\overline{\nu }}_{\ell }$ decays based on $417{\mathrm{fb}}^{-1}$ of data collected at the $\mathit{{\rm Y}}(4S)$ resonance with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ storage rings. Events are selected by fully reconstructing one of the $B$ mesons in a hadronic decay mode. A fit to the invariant mass differences $m(D^{(*)}\pi )-m(D^{(*)})$ is performed to extract the signal yields of the different $D^{**}$ states. We observe the $\overline{B}\to D^{**}{\ell }^{-}{\overline{\nu }}_{\ell }$ decay modes corresponding to the four $D^{**}$ states predicted by heavy quark symmetry with a significance greater than 5 standard deviations including systematic uncertainties.

Figure 1

Fit to the $m(D^{(*)}\pi )-m(D^{(*)})$ distribution for (a) $B^{-}\to D^{*+}{\pi }^{-}{\ell }^{-}{\overline{\nu }}_{\ell }$, (b) $B^{-}\to D^{+}{\pi }^{-}{\ell }^{-}{\overline{\nu }}_{\ell }$, (c) ${\overline{B}}^0\to D^{*0}{\pi }^{+}{\ell }^{-}{\overline{\nu }}_{\ell }$, and (d) ${\overline{B}}^0\to D^0{\pi }^{+}{\ell }^{-}{\overline{\nu }}_{\ell }$: the data (points with error bars) are compared to the results of the overall fit (sum of the solid distributions). The PDFs for the different fit components are stacked and shown in different colors.