Photoexcitation of the S-11(1535)-resonance on the proton, on the neutron, and in nuclei

The photoexcitation of the S-11(1535)-resonance has been studied in detail via photoproduction of eta-mesons at the Maine electron accelerator with the TAPS photon detector. The p(gamma,eta)p-reaction is used to study the excitation of the S-11(1535) on the free nucleon. Quasifree eta-photoproduction on deuterium is explored for a comparison of the p(gamma,eta)p and n(gamma,eta)n-cross sections. These data together with an upper limit for the d(gamma,eta)d-reaction allow a complete determination of the electromagnetic helicity amplitudes of the S-11(1535)-<N transition. Quasifree eta-photoproduction from nuclei (C-12, Ca-40, Nb-93, Pb-nat) is used for a study of the excitation of the S-11(1535)-resonance in the nuclear medium. The results are discussed in view of the recent debate about the status of this resonance.