Study of nucleon resonances in nuclei through(γ, η)and(γ, ρη)reactions

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(1) We have analyzed experimental data of the C, Al, Cu(γ, η) reactions, obtained at the Electron Synchrotron facility of INS.The deduced reaction cross sections show a broad resonance structure with a peak at around 900 MeV, for the first time. It is concluded that the resonance corresponds to the excitation and decay of the S_<11>(1535) resonance in a nucleus.(2) We have calculated the cross sections of (γ, η) reactions based on the quantum molecular dynamics model. The experimental data were compared with the calculations, and a possibility that the S11 resonance in nuclear medium becomes wider than in vacuum is suggested in the comparisons. In order to conclude definitely, however, much experimental work is needed to get more accurate data in detail.(3) We have constructed the STB Tagger at Laboratory of Nuclear Science in Tohoku University, which produces GeV tagged photons of good quality from the STB ring.(4) In order to measure η-mesons efficiently, we have designed and constracted a multi-detector system called SCISSORS, which consists of more than 200 pure CsI scintillators.(5) We have measured η Photoproduction reactions on nuclear targets using photon beams from the STB Tagger with SCISSORS.Excitation functions of the cross sections of (γ, η) reactions were decuced with much better statistics. The data are being analyzed now.(6) We have developed a solid hydrogen target in order to measure the H(γ, η) reaction, and succeeded to make a large volume of solid hydrogen, such as 30mm x 30mm x 40mm.