The radiative decays B→ Vγ at next-to-leading order in QCD

Abstract

We provide a model-independent framework for the analysis of the radiative B-meson decays B→K ∗γ and B→ ργ. In particular, we give a systematic discussion of the various contributions to these exclusive processes based on the heavy-quark limit of QCD. We propose a novel factorization formula for the consistent treatment of B→ Vγ matrix elements involving charm (or up-quark) loops, which contribute at leading power in Λ QCD/ m B to the decay amplitude. Annihilation topologies are shown to be power suppressed. In some cases they are nevertheless calculable. The approach is similar to the framework of QCD factorization that has recently been formulated for two-body non-leptonic B decays. These results allow us, for the first time, to compute exclusive b→ s( d) γ decays systematically beyond the leading logarithmic approximation. We present results for these decays complete to next-to-leading order in QCD and to leading order in the heavy-quark limit. Phenomenological implications for various observables of interest are discussed, including direct CP violation, and isospin and U-spin breaking effects.