Radiative Decays of Heavy Mesons and the Determination of the Strong g-Coupling

Abstract

The strong g-coupling characterizes the interaction of heavy mesons with pions in typical vertices $H^{\ast }H\pi$, $H^{\ast }{H}^{\ast }\pi$, where $(H^{\ast };H)$ stands for vector and pseudoscalar $(B^{\ast };B)$ or $(D^{\ast };D)$ heavy mesons. Its estimation by different theoretical methods has led to a wide range of possible values. We describe a new approach to the determination of g, which exploits the rare radiative decays $B^{\ast }\to B\gamma \gamma$ and $D^{\ast }\to D\gamma \gamma$. It is shown that the branching ratio of $D^{\ast }\to D\gamma \gamma$ can be expressed as a function of a single unknown $g$ and we calculate it to be in the measurable range between $1.6\times 10^{-6}$ and $3.3\times 10^{-5}$ for 0.25 < g < 1.

Comments: Lecture presented at the XXXIX Cracow School of Theoretical Physics, May 29-June 8, 1999, Zakopane, Poland