${\chi }_c$ decays and the gluon content of the ${\eta }^{\mathrm{\prime }}$, $\eta$ mesons

The large mass of the ${\eta }^{\mathrm{\prime }}$ meson indicates that a sizeable gluon component is present in the meson wave function. However, the ${\chi }_{c0}$ and ${\chi }_{c2}$ decays to ${\eta }^{\mathrm{\prime }}$ mesons, which proceed via a purely gluonic intermediate state and we would therefore na"{i}vely expect to be enhanced by such a component, are in fact relatively suppressed. We argue that this apparent contradiction may be resolved by a proper treatment of interference effects in the decay. In particular, by accounting for the destructive interference between the quark and gluon components of the ${\eta }^{\mathrm{\prime }}$ distribution function, in combination with a model for strange quark mass effects, we demonstrate that the observed ${\chi }_{c(0,2)}\to \eta {(}^{\mathrm{\prime }})\eta {(}^{\mathrm{\prime }})$ branching ratios can be reproduced for a reasonable gluon component of the ${\eta }^{\mathrm{\prime }}$, $\eta$ mesons.