Vector dominance effects in weak radiative decays ofBmesons

The long-distance vector-meson-dominance (VMD) effects on the weak radiative decays B¯→ργ and B¯ ${}_{}{}^0{}_{}{}^{}\mathit{D}_{}^{\mathrm{*}0}{}_{}{}^{}$γ are studied. For B¯→ργ decays, the VMD contribution is (10–20)% of the short-distance penguin amplitude. The pole effect is as important as the VMD one in the decay ${\mathit{B}}^{\mathrm{-}}$→${\mathrm{\rho }}^{\mathrm{-}}$γ, but it is suppressed in B¯ ${}_{}{}^0{}_{}{}^{}\mathrm{\rho }_{}^0{}_{}{}^{}$γ. The branching ratio of B¯→ργ, estimated to be of order ${10}^{\mathrm{-}6}$, strongly depends on the sign of the Wolfenstein parameter ρ. A measurement of any deviation of the ratio R=Γ(${\mathit{B}}^{\mathrm{-}}$→${\mathrm{\rho }}^{\mathrm{-}}$γ)/Γ(B¯ ${}_{}{}^0{}_{}{}^{}\mathrm{\rho }_{}^0{}_{}{}^{}$γ) away from the isospin value 2 will provide a probe on the long-range contribution and possibly indicate the sign of ρ: R>2 for ρ0. The decay B¯ ${}_{}{}^0{}_{}{}^{}\mathit{D}_{}^{\mathrm{*}0}{}_{}{}^{}$γ does not receive short-distance contributions, and its branching ratio, predicted to be 0.9×${10}^{\mathrm{-}6}$, is dominated by W exchange accompanied by a photon emission.