The isobar model of the γN → ηN processes is constructed on the basis of the precision measurements of the cross section for the γp → ηp process near the threshold in Mainz (Germany) and the sensational results of recent measurements of the Σ beam asymmetry and dσ/dΩ for this process in Grenoble (France). The model involves six nucleon resonances (MeV): S11(1535), S11(1650), P11(1440), P13(1720), D13(1520), and F15(1680). The properties of these resonances are discussed. The P13(1720) and F15(1680) resonances are responsible for large positive values of the Σ beam asymmetry for the γp → ηp reaction at small angles. The contribution of the S11(1650) resonance must be taken into account in addition to the contribution of the S11(1535) resonance in order to describe the experimental dependence of the total cross section on the photon energy. The values characterizing the γn → ηn reaction are calculated on the basis of the available data on the amplitudes of electromagnetic excitation of these resonances on protons and neutrons.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Nuclear and High Energy Physics