New calculations for incoherent eta photoproduction on nuclei including nonlocal and medium effects Original Research Article

The relativistic amplitude for the incoherent photoproduction of η mesons on nuclei is calculated taking into account the nonlocal effects in the propagation of the S11 resonance and the nucleon Born terms. The effects of the possible changes in the S11 properties in the nuclear medium are also investigated within the nonlocal approach. Taking 12C as example, it is found that the nonlocality leads to a slight increase of the cross section to isovector states at photon energies near threshold and decreases the cross section at higher energies. The size of these effects depends on the final state interactions of the η meson. For excitation of the isoscalar states the nonlocality effects are small, consistent with the small contributions of the S11 to these excitations. Density dependent broadening of the width leads to moderate suppression of the cross section for isovector states. Density dependent reduction in mass also leads to reduced incoherent cross sections.