Two-photon decays and photoproduction on electrons of $\eta(550)$,   $\eta'(958)$, $\eta(1295)$, and $\eta(1475)$ mesons
  Electromagnetic interactions of the ground and first radial excited states of $\eta$ and $\eta'$ mesons in the framework of the extended $U(3)\times U(3)$ NJL model are considered. The radial excitations are described with the help of polynomial form factor of the second order over the inner quark momentum. The solution of the $U_A(1)$ problem by means of 't Hooft interaction is taken into account. For diagonalization of the free Lagrangian the $4\times4$ mixing matrix is used. Two-photon decay widths of the ground $\eta$ and $\eta'$ meson are found to be in a satisfactory agreement with the experiment. Predictions for the two-photon decay widths of $\eta(1295)$ and $\eta(1475)$ are given. The probabilities of eta meson production by two-photon mechanism in $e^+e^-$ collisions and of their photoproduction on electrons are calculated. 
A. B. Arbuzov, M. K. Volkov
hep-ph