Semi-inclusive B Decays and Direct CP Violation in QCD Factorization

We have systematically investigated the semi-inclusive B decays B →MX, which are manifestations of the quark decay b → Mq, within the framework of QCD-improved factorization. These decays are theoretically clean and have distinctive experimental signatures. We focus on a class of these that do not require any form factor information and therefore may be especially suitable for extracting information on the angles α and γ of the unitarity triangle. The nonfactorizable effects, such as vertex-type and penguin-type corrections to the two-body b decay, b→Mq, and hard spectator corrections to the 3-body decay B → Mq1q̄2 are calculable in the heavy quark limit. QCD factorization is applicable when the emitted meson is a light meson or a charmonium. We discuss the issue of the CPT constraint on partial rate asymmetries. The strong phase coming from final-state rescattering due to hard gluon exchange between the final states can induce large rate asymmetries for tree-dominated color-suppressed modes (π0, ρ0, ω)Xs̄. The nonfactorizable hard spectator interactions in the 3-body decay B →Mq1q̄2, though phase-space suppressed, are extremely important for the tree-dominated modes (π0, ρ0, ω)Xs̄, φX, J/ψXs, J/ψX and the penguin-dominated mode ωXss̄. In fact, they are dominated by the hard spectator corrections. This is because the relevant hard spectator interaction is color allowed, whereas the two-body semi-inclusive decays for these modes are color-suppressed. Our result for B(B → J/ψXs) is in agreement with experiment. The semi-inclusive decay modes: B 0 s → (π0, ρ0, ω)Xs̄, ρXss̄, B 0 → (K−X,K∗−X) and B− → (K0Xs,K∗0Xs) are the most promising ones in searching for direct CP violation. In fact, they have branching ratios of order 10−6 − 10−4 and CP rate asymmetries of order (10 − 40)%. The decays B 0 s → (π0, ρ0, ω)Xss̄ and B− → φX are electroweak-penguin dominated. Some of them have sizable branching ratios and observable CP asymmetries.