B-->J/ψ K decays in QCD factorization

The hadronic decays B-->J/ψK(K^*) are interesting because experimentally they are the only color-suppressed modes which have been measured, and theoretically they are calculable by QCD factorization even when the emitted meson J/ψ is heavy. We analyze the decay B-->J/ψK within the framework of QCD factorization. We show explicitly the scale and γ₅-scheme independence of decay amplitudes and infrared safety of nonfactorizable corrections at twist-2 order. Leading-twist contributions from the light-cone distribution amplitudes (LCDAs) of the mesons are too small to accommodate the data; the nonfactorizable corrections to naive factorization are small. We study the twist-3 effects due to the kaon and find that the coefficient a₂(J/ψK) is largely enhanced by the nonfactorizable spectator interactions arising from the twist-3 kaon LCDA φ^K_σ, which are formally power suppressed but chirally, logarithmically, and kinematically enhanced. Therefore, factorization breaks down at twist-3 order. The higher-twist effects of J/ψ are briefly discussed. Our result also resolves the long-standing sign ambiguity of a₂(J/ψK), which turns out to be positive for its real part.