Power Corrections in Charmless Nonleptonic B Decays: Annihilation is Factorizable and Real

We classify ΛQCD/mb power corrections to nonleptonic B → M1M2 decays, where M1,2 are charmless non-isosinglet mesons. Using recent developments in soft-collinear effective theory, we prove that the leading contributions to annihilation amplitudes of order αs(mb) ΛQCD/mb are real. The leading annihilation amplitudes depend on twist-2 and the twist-3 three parton distributions. A complex nonperturbative parameter from annihilation first appears at (Omega)[αs2(√Λmb)ΛQCD/mb]. 'Chirally enhanced' contributions are also factorizable and real at lowest order. Thus, incalculable strong phases are suppressed in annihilation amplitudes, unless the αs(√Λmb) expansion breaks down. Modeling the distribution functions, we find that (11 ± 9)% and (15 ± 11)% of the absolute values of the measured (bar B)0 → K-π+ and B- → K-K0 penguin amplitudes come from annihilation. This is consistent with the expected size of power corrections