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

Comments: 12 pages, 1 figure, 3 tables, version published in JHEP