Unitarity, analyticity and duality constraints in η and π photoproduction

We report an update of the isobar model EtaMAID. A new approach is proposed to avoid double counting in the overlap region of Regge and resonances. Dispersion relation is applied on top of the isobar model, and both models describe the data equally well. Application of these ideas to pion photoproduction is discussed.

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

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.