Proton-induced production of eta on nuclei.

Abstract

The features of the (p,p'\ensuremath{\eta}) reaction are examined for incident proton energies between 0.8 and 1.6 GeV. Reactions are calculated for exclusive transitions in which the continuum proton and \ensuremath{\eta} are observed in coincidence. This process should be dominated by transitions N+N\ensuremath{\rightarrow}N+N+\ensuremath{\eta} involving intermediate excitation of one of the nucleons to an N(1535) isobar. We take phenomenological amplitudes for the process \ensuremath{\pi}+N\ensuremath{\rightarrow}\ensuremath{\eta}+N in the nuclear medium. A theoretical formalism for the reaction amplitudes is derived and examined in detail. Nuclear distortions of the hadrons are estimated in the eikonal approximation. The theoretical cross sections are shown to be dominated by a single production amplitude. This results in the prediction that \ensuremath{\eta} production should occur entirely through \ensuremath{\Delta}T=1 non-normal parity nuclear transitions; i.e., that the nuclear states excited should show the spin-isospin characteristics of the exchanged meson. Peak reaction cross sections are predicted to have a strong dependence on the incident proton energy. Expected peak cross sections, for a target like $^{16}\mathrm{O}$, are on the order of 1 \ensuremath{\mu}b/${\mathrm{sr}}^{2}$ MeV.