Branching ratio and direct CP-violating rate asymmetry of the rare decays B → K ∗γ and B → ϱγ

We calculate CP-violating rate asymmetries in the rare radiative decays B ^± → K ^∗±γ and B^± → ϱ^±γ. They arise because of the interference between leading-order penguin amplitudes and one-gluon corrections with absorptive phases, and provide unambiguous evidence for direct CP violation. Complementing earlier studies, we also investigate gluon exchange with the 'spectator' quark. The bound state effects in the exclusive matrix elements are taken into account by a covariant model, which yields a branching ratio BR(B → K ^∗γ) = (4 - 5) × 10 ^-5 in good agreement with the observed value. The bound state effects increase the CP asymmetry, which is of order 1% in the channel B → K ^∗γ and 15% for B → ϱγ.