Study of S11 resonance in nuclei through (γ, η) reactions Original Research Article

In order to study the S11(1535) resonance in the nuclear medium, total cross sections of the (γ, η) reactions on C, Al and Cu have been measured for photon energies between 680 and 1000 MeV. A broad resonance due to the excitation and decay of the S11 resonance in the nucleus has been clearly observed for the first time. The apparent energy and width of the resonance are 900 and 300 MeV, respectively. Model calculations based on the quantum molecular dynamics have been performed. A comparison of the calculations with the data indicates that the S11 resonance in nuclei should have a larger width; the width of about 250 MeV is required while the elementary one is about 150 MeV.