Photoproduction of $\eta$-mesons off C and Cu nuclei for photon energies below 1.1 GeV

The $\eta$-meson photoproduction cross sections have been measured on the C and Cu targets for the photon energies between 600 and 1100 MeV to investigate the behavior of the $S_{11}$(1535) resonance in a nucleus. The excitation functions of the cross section as well as the angular and momentum distributions of $\eta$-mesons are in quantitative agreement with the Quantum Molecular Dynamics (QMD) model calculations in which the $\eta$-meson emission processes other than the $S_{11}$(1535) resonance are also incorporated as proposed in the $\eta$-MAID model. It is shown that the excitation of the $D_{15}$(1675) resonance might play an important role for $E_{\gamma}>900$ MeV.
Comment: 16 pages 4 figures, submitted to Phys. Lett. B