There are two apparent puzzles connected with the two-body and three-body doubly charmed baryonic $B$ decays. First, earlier calculations based on QCD sum rules or the diquark model predict $\mathcal{B}({\overline{B}}^0\to {\Xi }_c^{+}{\overline{\Lambda }}_c^{-})\approx \mathcal{B}({\overline{B}}^0\to {\mathcal{B}}_c\overline{N})$, while experimentally the former has a rate 2 orders of magnitude larger than the latter. Second, a naive estimate of the branching ratio $\mathcal{O}({10}^{-9})$ for the color-suppressed three-body decay $\overline{B}\to {\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}K$, which is highly suppressed by phase space, is too small by 5 to 6 orders of magnitude compared to the experiment. We show that the great suppression for the ${\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}K$ production can be alleviated provided that there exists a narrow hidden charm bound state with a mass near the ${\Lambda }_c{\overline{\Lambda }}_c$ threshold. This new state that couples strongly to the charmed baryon pair can be searched for in $B$ decays and in $p\overline{p}$ collisions by studying the mass spectrum of $D^{(*)}{\overline{D}}^{(*)}$ or ${\Lambda }_c{\overline{\Lambda }}_c$. The doubly charmful decay $\overline{B}\to {\Xi }_c{\overline{\Lambda }}_c$ has a configuration more favorable than the singly charmful one such as ${\overline{B}}^0\to {\Lambda }_c\overline{p}$ since no hard gluon is needed to produce the energetic ${\Xi }_c{\overline{\Lambda }}_c$ pair in the former decay, while two hard gluons are needed for the latter process. Assuming that a soft $q\overline{q}$ quark pair is produced through the $\sigma$ and $\pi$ meson exchanges in the configuration for $\overline{B}\to {\Xi }_c{\overline{\Lambda }}_c$, it is found that its branching ratio is of order ${10}^{-3}$, in agreement with the experiment.

• Received 29 December 2005

DOI:https://doi.org/10.1103/PhysRevD.73.074015