Study of $B^{-}\to \mathrm{\Lambda }\bar{p}{\eta }^{{(}^{\mathrm{\prime }})}$ and ${\bar{B}}_s^0\to \mathrm{\Lambda }\bar{\mathrm{\Lambda }}{\eta }^{{(}^{\mathrm{\prime }})}$ decays

We study the three-body baryonic $B\to \mathbf{B}{\bar{\mathbf{B}}}^{\mathbf{\prime }}M$ decays with $M$ representing the $\eta$ or ${\eta }^{\mathrm{\prime }}$ meson. Particularly, we predict that ${\cal B}(B^-\to\Lambda\bar p\eta,\Lambda\bar p\eta’)=(5.3\pm 1.4,3.3\pm 0.7)\times 10^{-6}$or$(4.0\pm 0.7,4.6\pm 1.1)\times 10^{-6}$, where the errors arise from the non-factorizable effects as well as the uncertainties in the $0\to {\bf B\bar B’}$and$B\to{\bf B\bar B’}$ transition form factors, while the two different results are due to overall relative signs between the form factors, causing the constructive and destructive interference effects. For the corresponding baryonic ${\bar{B}}_s^0$ decays, we find that ${\cal B}(\bar B^0_s\to \Lambda\bar \Lambda \eta,\Lambda\bar \Lambda \eta’)=(1.2\pm 0.3,2.6\pm 0.8)\times 10^{-6}$or$(2.1\pm 0.6,1.5\pm 0.4)\times 10^{-6}$ with the errors similar to those above. The decays in question are accessible to the experiments at BELLE and LHCb.