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Charmless Two-body Baryonic $B_{u,d,s}$ Decays Revisited

We study charmless two-body baryonic $B$ decays using the topological amplitude approach. We extend a previous work to include all ground state octet and decuplet final states with full topological amplitudes. Relations on rates and CP asymmetries are obtained. The number of independent topological amplitudes is significantly reduced in the large $m_B$ asymptotic limit. With the long awaited $\overline B{}^0\to p\bar p$ data, we can finally extract information on the topological amplitudes and predict rates of all other modes. The predicted rates are in general with uncertainties of a factor of two by including corrections to the asymptotic relations and from sub-leading contributions. We point out some modes that will cascadely decay to all charged final states and have large decay rates. For example, $\overline B {}^0_s\toΩ^-\overline{Ω^-}$, $B^-\to p\overline{Δ^{++}}$, $B^-\to Λ\bar p$ and $\overline B{}^0_s\to Λ\overlineΛ$ decays are interesting modes to search for. We find that the $\overline B{}^0\to p\bar p$ mode is the most accessible one among octet-anti-octet final states in the $ΔS=0$ transition. It is not surprise that it is the first one being found. With the detection of $π^0$ and/or $γ$ many other unsuppressed modes can be searched for. The predicted $\overline B{}^0_s\to p\bar p$ rate is several order smaller than the present experimental result. The central value of the experimental result can be reproduced only with unnaturally scaled up "subleading contributions", which will affect other modes including the $\overline B{}^0\to p\bar p$ decay. We need more data to clarify the situation. The analysis presented in this work can be systematically improved when more measurements on decay rates become available.