Study Of The Nucleon Resonances Within An Effective Lagrangian Approach

Hadron physics is already an important part of nuclear physics, the basic particle physics and astrophysics. And the hadron spectroscopy as the study of hadron mass spectrum and the classification of hadron is an important part of particle physics. The study of the spectrum of the baryon resonances and the resonances coupling constants from the available experimental data are two of the most important issues in hadronic spectroscopy and they are attracting much attention. As one of the research hotspots in hadron spectroscopy, the baryon reso-nances in the framework of quark model has two outstanding difficulties at present. One is serious discrepancy between the prediction of some lowest excited states quality and exper-iment, another difficulty is that the predictions of the number of excited state is far greater than the experimental measurement results. Therefore, in order to further deepen the un-derstanding of hadron structure and the quark model so as to solve the present difficulties, the study of the baryon resonances is meaningful and necessary.This article mainly introduces how to investigate nucleon resonances within an effective Lagrangian approach and the isobar model. Compared with the partial wave analysis, using effective Lagrangian approach can get clearer property of some nucleon resonances, and in-dividual resonance contributions are more easy to pin down. Firstly, we need to construct vertex effective Lagrangian. After that, using these vertex effective Lagrangian can get reac-tion amplitudes. And using these reaction amplitudes can also get the differential reaction cross section and total reaction cross section formula. Then we can fit the phases between individual resonance and the unknown coupling constants by using the differential reaction cross section experimental data. Finally we can use the results to study nucleon resonances.This article is divided into four chapters. The first chapter is the introduction part, introducing simply the history of particle physics and the status quo of hadron physics. The second chapter mainly introduces some basic theories of particle physics and the research background of baryon excited states. The third chapter mainly introduces how to investigate nucleon resonances within an effective Lagrangian approach and the isobar model. The fourth chapter summarize the whole paper, and points out the advantages and shortages of the effective Lagrangian approach.