Determination of the strong g-coupling and of the μ B * B γ - strength from two-photon decays of heavy vector mesons

Abstract

We describe a calculation of the two-photon decays of heavy vector-mesons, B * → Bγγ and D * → Dγγ, by using the “heavy meson chiral Lagrangian”. The decay amplitudes are expressed in terms of the strong coupling g of the Lagrangian at various powers and the strength of the anomalous magnetic dipole μ B * B γ (respectively μ D * D γ). In the charm case we are able to express the branching ratio Γ( D *0 → D 0γγ)/Γ( D *0) as a function of g only and we expect it to be in the 10 −6 − 10 −5 range, depending on the value of g. The determination of μ B *0 B 0γ , μ B *+ B+ γ requires a more involved analysis, including the consideration of bremsstrahlung radiation for the B *+ → B +γγ case.