Photoproduction of eta and eta ' mesons off nucleons close to threshold

The importance of Born terms and resonance exchange for eta and eta' photop roduction off both the proton and neutron within U(3) baryon chiral perturb ation theory is investigated. Low-lying resonances such as the vector meson s and J(P) = 1/2(+), 1/2(-) baryon resonances are included explicitly and t heir contributions together with the Born terms are calculated. The couplin g constants of the resonances are determined from strong and radiative deca ys. We obtain reasonable agreement with experimental data near threshold.