The $\eta$NN Coupling in Eta Photoproduction

Low-energy eta photoproduction on the nucleon is studied in an effective Lagrangian approach that contains Born terms, vector meson and nucleon resonance contributions. The resonance sector includes the $S_{11}(1535)$, $P_{11}(1440)$ and $D_{13}(1520)$ states whose couplings are fixed by independent electromagnetic and hadronic data. The available $(\gamma,\eta)$ data are employed to discuss the difference between pseudoscalar and pseudovector Born terms and to determine the magnitude of the $\eta NN$ coupling constant. We present multipoles that are most sensitive to the various model ingredients and demonstrate how these multipoles may be accessed in polarization observables. Cross section calculations are presented for eta photoproduction on light nuclei.