Production of eta and eta` mesons on nucleons and nuclei

The production of eta and eta` mesons in photon- and hadron-induced reactions on free and quasi-free nucleons and on nuclei is reviewed. The extensive database on gamma N -> eta N, for both proton and neutron targets, is described in detail and its implications for the search for N* resonances much heavier than the dominant S-11(1535) discussed. Though less is currently known about the production of the eta` or of eta pi pairs, these also offer tantalizing prospects in the search for the missing isobars. The more limited data available on pion-induced production are still necessary ingredients in the partial wave analysis discussed. The production of the eta-meson in pp and pn collisions shows once again the strong influence of the S-11(1535) isobar, which is in contrast to the relatively weak behaviour seen near threshold for eta` production. This difference is reflected in the important final State interaction effects of the eta in nuclei that may even lead to this meson being ``bound`` in some systems. The evidence for this is reviewed for both gamma A and pA collisions. The inclusive photoproduction of eta, eta`, and eta pi pairs from nuclei provides further information regarding the production mechanism and the interaction of the eta and eta` with nuclei and the eta pi pairs may even allow access to low mass eta A systems that are forbidden in direct single-meson photoproduction. (C) 2014 Elsevier B.V. All rights reserved.