The $X(3872) \to J/\psi \gamma$ decay in the $D \bar D^*$ molecular picture

Abstract

From a picture of the X(3872) where the resonance is a bound state of $\bar{D}D^*-c.c.$, we evaluate the decay width into the $J/\psi \gamma$ channel, which is sensitive to the internal structure of this state. For this purpose we evaluate the loops through which the X(3872) decays into its components, and the $J/\psi$ and the photon are radiated from these components. We use the local hidden gauge approach extrapolated to SU(4) with a particular SU(4) breaking. The radiative decay involves anomalous couplings and we obtain acceptable values which are compared to experiments and results of other calculations. Simultaneusly, we evaluate the decay rate for the X(3872) into $J/\psi \omega$ and $J/\psi \rho$, and the results obtained for the ratio of these decay widths are compatible with the experiment. We also show the grossly unacceptable results that come from taking only the $\bar{D}^0D^{*0}+c.c.$ component.