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

Abstract

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