Determination of the strong g-coupling and of the $μ_{B^*Bγ}-$ strength from two-photon decays of heavy vector mesons

Abstract

We describe a calculation of the two-photon decays of heavy vector-mesons, $B^*\to Bγγ$ and $D^*\to Dγγ$, 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 $μ_{B^*Bγ}$ (respectively $μ_{D^*D}γ$). In the charm case we are able to express the branching ratio $Γ(D^{*0}\to D^0γγ)/Γ(D^{*0})$ 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 $μ_{B^{*0}B^{0}γ},μ_{B^{*+}B^+}γ$ requires a more involved analysis, including the consideration of bremsstrahlung radiation for the $B^{*+}\to B^+γγ$ case.