Abstract
We study the direct CP-violating asymmetries (CPAs) in the two-body A b decays. We explain the observed decay branching ratios of Λ b → (pK - , pπ - ), and find that their corresponding direct CPAs are (5.8±0.2, -3.9±0.2)%. For Λ b → (pK ∗- , pp - ), the decay branching ratios and CPAs in the Standard Model are predicted to be (2.5 ±0.5, 11.4 ±2.1) × 10 -6 and (19.6 ± 1.6, - 3.7 ± 0.3)%, respectively. We point out that the large CPA for Λ b → pK ∗- is promising to be measured by the CDF and LHCb experiments.