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

核研究的一个重要挑战是理解QCD中的强子结构。进行这一研究的途径之一是研究核子共振的电磁跃迁形状因子。该项目的目的是提取过渡形式因素。从<33><S11>介子电生的实验数据出发，导出了Δ_和N^*_共振的计算公式，本文用么正变换的方法，从介子和重子的相互作用哈密顿量出发，建立了一个电生介子的动力学反应模型。计算结果与Jlab，Mainz和MIT-Bates的实验数据吻合较好，主要结果如下：1. NΔ跃迁的磁偶极（M1）形状因子通过非共振再散射机制对NΔ形状因子的修正，解释了经验获得的M1形状因子与夸克模型预测之间长期存在的差异以及形状因子对动量的软依赖性. NΔ跃迁的电四极（E_2，C_2）形状因子表明存在着反映核子和δ形变的E_2和C_2形状因子。在高动量传递区，E1/M1比远小于pQCD的预测。在低动量转移区域，我们预测了一个大的贡献从π介子电流。在S_<11>区，我们发展了描述两π介子质子过程的有效哈密顿量，并发展了一种数值方法来克服三体散射态的Wick旋转带来的困难，总之，我们表明了动力学方法在从电弱反应数据中提取核子共振信息方面的重要性。

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.