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

Abstract

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

Comments: Invited lecture presented by P. Singer at IV Intern.Conference on Hyperons,Charm and Beauty Hadrons,June27-30,2000,Valencia,Spain. Submitted to Nucl. Phys. B