Inclusive photoproduction of η mesons on complex nuclei

Abstract

A relativistic model for the inclusive photoproduction of \ensuremath{\eta} mesons on complex nuclei is introduced. The elementary production process is described using an effective Lagrangian approach. Contributions from several nucleon resonances in the second resonance region, as well as the Born and vector meson terms, are taken into account. The dynamics of nucleon motion are based on the relativistic mean field theory of Walecka. The \ensuremath{\eta} mesons are described by solutions of the Klein-Gordon equation. It is assumed that the inclusive process results from quasifree photoproduction on individual nucleons; the inclusive cross sections are obtained by integrating a set of exclusive quasifree cross sections. Distortion effects due to final state interactions of the outgoing \ensuremath{\eta} are taken into account. The calculated cross sections are compared with the available experimental data on ${}^{12}\mathrm{C}$ and ${}^{40}\mathrm{Ca},$ for photon energies from near threshold to about 800 MeV. The plane wave calculations are found to lie consistently above the data. Distortion effects lead to a strong suppression of the cross sections. Agreement with experiment is lacking when a set of parameters obtained from older data for the elementary process is used. The level of agreement is much improved when parameters based on recent elementary cross section data are used.