S11(1535) Resonance in Nuclei Studied via (γ,η) Reactions

The properties of the S11(1535) resonance in nuclei were studied through the C(γ, η) reaction for 600 ≪ Eγ≪ 1100 MeV. The excitation function of the cross section shows a broad resonance structure peaked around 900 MeV with a width of more than 300 MeV, which is originated from the S11(1535) resonance. The QMD model calculation with the standard parameter of the S11(1535) resonance underestimates the yields for Eγ larger than 850 MeV. In order to reproduce the shape of the broad resonance structure, an artificial modification of the resonance parameter of the S11(1535) is necessary; the helicity amplitude should be increased by 6 % or the resonance width should be increased by 70 MeV.