Testing the W -exchange mechanism with two-body baryonic B decays

Abstract

The role of W -exchange diagrams in baryonic B decays is poorly understood, and often taken as insignificant and neglected. We show that charmful two-body baryonic $B\to {\mathbf{B}}_c\overline{\mathbf{B}}\prime$ decays provide a good test-bed for the study of the W -exchange topology, whose contribution is found to be non-negligible; here B_c is an anti-triplet or a sextet charmed baryon, and $\overline{\mathbf{B}}\prime$ an octet charmless (anti-)baryon. In particular, we calculate that $\mathrm{ℬ}\left({\overline{B}}^0\to {\mathrm{\Sigma }}_c^{+}\overline{p}\right)=\left({2.9}_{-0.9}^{+0.8}\right)\times {10}^{-6}$ in good agreement with the experimental upper bound. Its cousin ${\overline{B}}_s^0$ mode, ${\overline{B}}_s^0\to {\mathrm{\Lambda }}_c^{+}\overline{p}$, is a purely W -exchange decay, hence is naturally suited for the study of the role of the W -exchange topology. We predict $\mathrm{ℬ}\left({\overline{B}}_s^0\to {\mathrm{\Lambda }}_c^{+}\overline{p}\right)=\left(0.8\pm 0.3\right)\times {10}^{-6}$, a relatively large branching ratio to be tested with a future measurement by the LHCb collaboration. Other predictions, such as $\mathrm{ℬ}\left({\overline{B}}^0\to {\mathrm{\Xi }}_c^{+}{\overline{\mathrm{\Sigma }}}^{-}\right)=\left(1.1\pm 0.4\right)\times {10}^{-5}$, can be tested with future Belle II measurements.