Search for $\overline{B}\to {\Lambda }_c^{+}X{\ell }^{-}{\overline{\nu }}_{\ell }$ decays in events with a fully reconstructed $B$ meson

We present a search for semileptonic $B$ decays to the charmed baryon ${\Lambda }_c^{+}$ based on $420{\mathrm{fb}}^{-1}$ of data collected at the ${\rm Y}(4S)$ resonance with the BABAR detector at the PEP-II $e^{+}{e}^{-}$ storage rings. By fully reconstructing the recoiling $B$ in a hadronic decay mode, we reduce non-$B$ backgrounds and determine the flavor of the signal $B$. We statistically correct the flavor for the effect of the $B^0$ mixing. We obtain a 90% confidence level upper limit of $\mathcal{B}(\overline{B}\to {\Lambda }_c^{+}X{\ell }^{-}{\overline{\nu }}_{\ell })/\mathcal{B}(\overline{B}\to {\Lambda }_c^{+}X)<3.5\%$.

Figure 1

Feynman diagrams for $B$ decays into a charmed baryon through external $W$ emission (a) and internal $W$ emission (b).

Figure 2

Fit to the ${\Lambda }_c^{+}$ candidate mass distribution for $\overline{B}\to {\Lambda }_c^{+}X{e}^{-}{\overline{\nu }}_e$ (a) and $\overline{B}\to {\Lambda }_c^{+}X{\mu }^{-}{\overline{\nu }}_{\mu }$ (b). The data are shown as points with error bars, the overall fit as a solid line, and the peaking background contribution as a cross-hatched area. The combinatorial $B\overline{B}$ and continuum background is shown as the area below the dotted line.

Figure 3

Fit to the ${\Lambda }_c^{+}$ candidate mass distribution for $\overline{B}\to {\Lambda }_c^{+}X$. The data are shown as points with error bars, the overall fit as a solid line, and the combinatorial $B\overline{B}$ and continuum background as a dashed line.