Power corrections in charmless nonleptonic B decays:: Annihilation is factorizable and real

We classify Lambda(QCD)/m(b) power corrections to nonleptonic B -> M1M2 decays, where M-1,M-2 are charmless nonisosinglet mesons. Using recent developments in soft- collinear effective theory, we prove that the leading contributions to annihilation amplitudes of order alpha(s) (m(b)) Lambda(QCD)/m(b) are real. The leading annihilation amplitudes depend on twist- 2 and twist- 3 three- parton distributions. A complex nonperturbative parameter from annihilation first appears at O[alpha(2)(s) (root Lambda m(b)) Lambda(QCD)/m(b)]. "Chirally enhanced'' contributions are also factorizable and real at lowest order. Thus, incalculable strong phases are suppressed in annihilation amplitudes, unless the alpha(s)(root Lambda m(b)) expansion breaks down. Modeling the distribution functions, we find that (11 +/- 9)% and (15 +/- 11)% of the absolute values of the measured (B) over bar (0) -> K- pi(+) and B- -> K- K-0 penguin amplitudes come from annihilation. This is consistent with the expected size of power corrections.