Long-distance effects in B -> V gamma radiative weak decays - art. no. 093002

A systematic approach to long-distance effects in exclusive radiative weak B decays is presented, based on a combination of the heavy quark limit with perturbative QCD. The dominant long-distance effects, connected with weak annihilation and W-exchange topologies, can be computed in a model-independ ent way using experimental data on B radiative leptonic decays. Nonfactoriz able corrections vanish in the chiral limit and to leading twist. The left- handed photon amplitudes are shown to be enhanced relative to the right-han ded ones, both in the long- and short-distance parts of the (B) over bar de cay amplitudes. Recent CLEO data on B-->K*gamma decays are consistent with standard model estimates of the long-distance contributions, and disfavor a n enhanced gluonic penguin contribution. We discuss the implications of our results for the extraction of \V-td\.