Eta and Etaprime Photoproduction on the Nucleon with the Isobar Model EtaMAID2018

摘要

The isobar model EtaMAID has been updated with new and high precision data for η and η′ photoproduction on protons and neutrons from MAMI, ELSA, GRAAL and CLAS. The background is described in a recently developed Regge-cut model, and for the resonance part the whole list of nucleon resonances has been investigated with 21 N * states contributing to η photoproduction and 12 N * states contributing to η′ photoproduction. Finally, the possibility of a narrow resonance near W = 1900 MeV is discussed, that would be able to explain unexpected energy and angular dependence of observables in p ( γ , η′ ) p near η threshold.