Is eta' partially made of gluonium?

Abstract

A phenomenological analysis of radiative $V\to P\gamma$ and $P\to V\gamma$ decays is performed in order to determine the gluonic content of the $\eta^\prime$ wave function. Our result shows that there is no evidence for such a gluonium contribution, $Z_{\eta^\prime}^2=0.04\pm 0.09$. In terms of a mixing angle description this corresponds to $\phi_P=(41.4\pm 1.3)^\circ$ and $|\phi_{\eta^\prime G}|=(12\pm 13)^\circ$.