Rates and CP asymmetries of charmless two-body baryonic B_(u,d,s) decays

摘要

With the experimental evidences of B 0→ pp and B~- →Λ p decays, it is now possible to extract both tree and penguin amplitudes of the charmless two-body baryonic B decays for the first time. The extracted penguin- tree ratio agrees with the expectation. Using the topological amplitude approach with the experimental results on B~ 0→ pp and B~- →Λ p decay rates as input, predictions on all other B_q → BB, BD, VB and VV decay rates, where B and D are the low lying octet and decuplet baryons, respectively, are given. It is nontrivial that the results do not violate any existing experimental upper limit. From the analysis it is understandable that why B~0→ pp and B~- →Λ p modes are the first two modes with experimental evidences. Relations on rates are verified using the numerical results. We note that the predicted B~- → pΔ~(++) rate is close to the experimental bound, which has not been updated in the last ten years. Direct CP asymmetries of all B_q → BB, BD, VB and DD modes are explored. Relations on CP asymmetries are examined using the numerical results. The direct CP asymmetry of B~0→ pp decay can be as large as ±50%. Some of the CP asymmetries can serve as tests of the Standard Model. Most of them are pure penguin modes, which are expected to be sensitive to new physics contributions. In particular, B_s~0 → Ξ~-Ξ~-, B~0 → Ξ~-Σ~(*-), B~0 → Ω~-Ξ~-, B_s~0 → Σ~(*-)Σ~(*-), S_s~0→ Ω~-Ω~-, S_s~0 →Ξ~-Ξ~(*-), B_s~0→ Ξ~ (*-)Ξ~-, B~0 →Ξ~(*-)Σ~(*-), B~0 →Ω~-Ξ~(*-) and B_s~0→ Ξ~(*-)Ξ~(*-) decays are AS = -1 pure penguin modes with unsup-pressed rates, which can be searched in the near future. Their CP asymmetries are constrained to be of few % and are good candidates to be added to the list of the tests of the Standard Model.