Phenomenological Evidence for the Gluon Content of $\eta$ and ${\eta }^{\prime }$

Abstract

We discuss the effect of $\eta$--${\eta }^{\prime }$ mixing and of axial current anomalies on various decay processes. We describe the 2$\gamma$ decays of $\eta$ and ${\eta }^{\prime }$, the radiative decays of low-lying vector mesons as well as the decays $\eta \to 3\pi$, $J/\psi \to \eta \gamma$ and $J/\psi \to {\eta }^{\prime }\gamma$ in one unified framework, in which they are related to the electromagnetic and strong axial current anomalies, respectively. We also discuss briefly the enhancement of ${\eta }^{\prime }$ in $D_s$ decays and suggest a possible relation to gluon-mediated processes. The importance of the decays of the glueball candidates $f_0(1500)$ and $f_0(1590)$ into $\eta {\eta }^{\prime }$ channels is also stressed.

Comments: 13 pages, Latex2e, 4 figures (uuencoded and gzipped)