Structure of N^*(1535) and Δ(1232) with Electromagnetic Probe

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An important challenge in nuclear research is to understand the hadron structure within QCD. One of the approach for pursuing this research is the study of the electromagnetic transition form factors of nucleon resonances. The purpose of this project is to extract the transition form factors. of Δ_<33> and N^*_<S11> resonances from the data of the electroproduction of meson.In this work we developed a dynamical reaction model on the electroproduction of mesons form the interaction Hamiltonian of meson and baryon with the method of unitary transformation. The predicted cross sections of the pion electropruduction were found to describe very well the extensive data from Jlab, Mainz and MIT-Bates.The results of our work are summarized as follows.1. Magnetic dipole(M1) form factor of NΔ transitionThe long standing discrepancy between empirically obtained M1 form factor and the prediction of quark models and also the very soft momentum dependence of the form factor were explained by the modification of the NΔ from factor due to the non-resonant rescattering mechanism.2. Electric quadrupole(E2,C2) form factor of NΔ transitionThe E2 and C2 form factors, which indicate the deformation of nucleon and delta, were shown to exist. In the high momentum transfer region the E1/M1 ratio was far small compared with the pQCD prediction. In the low momentum transfer region, we predicted a large contribution from the pion current. Those results have motivated proposal of new experiments.In the S_<11> region, we have developed effective Hamiltonian to describe two-pion prodo ion processes, and developed a numerical method to overcome difficulties due to the three-body scattering state using Wick-rotation.In summary we have shown the importance of dynamical approach to extract information on the nucleon resonance from the data of electroweak reactions.