Non-strange Light Baryon Spectrum In Constituent Quark Model

Hadronic spectrum is an ideal place to test strong interaction theory--quantum chromodynamics(QCD)and is also an important tool to recognize the internal structure of hadron.QCD has three basic features: asymptotic freedom,color confinement and spontaneous breaking of chiral symmetry.High energy process can be treated by employing perturbation QCD due to asymptotic freedom.However,in low energy region,QCD is high non-perturbative and therefore non-perturbative methods are needed for the low energy process.Now commonly adopted QCD effective theory or model includes lattice QCD,QCD sum rules,constituent quark model.The lattice QCD is still unable to calculate all the physical quantities with the current computation power due to its huge calculation work.The QCD sum rule is only applicable to the ground state.The constituent quark model can not only reduce the requirement of computer performance,but also can be applied to study the excited state as well as ground state of hadrons,which will be employed to study the non-strange light baryon spectrum in this thesis.In the constituent quark model,the quark-quark interaction is descripted by QCD-inspired potential.Due to the non-perturbation in the low energy region,it is impossible to obtain a complete potential in the whole range.At present,the most representative quark potential is Cornell potential and other quark potentials can be obtained by various corrections to Cornell potential.KMS potential is a corrected one by considering the color-screening effect due to light quark pair creation.It has been demonstrated that KMS potential can give more reasonable energy spectra for heavy flavor meson,in particular,for high excited states.In this thesis,we shall study the spectra of light baryons by using Cornell potential and KMS potential and give a comparison with experimental data.In the long-range region,the vector-scalar mixing confinement potential is adopted.The SU(6)symmetric bases are used to construct the wave function and of which the space wave function use the harmonic oscillator basis in Jacobian coordinates up to N=3 harmonic oscillator shell.Finally,it was found that KMS potential was more suitable for the calculation of the Light baryon spectrum,and it was proved that the negative parity could be mixed with the pentaquark component.The present calculations are limited only to non-strange light baryons,which can be extended in future work to other baryons or multiquark systems.This paper can be divided into the following parts:In the first part,the basic knowledge of particle physics is briefly introduced.In the second part,the component quark model is discussed in detail,and one-gluon exchange potential and confinement potential are obtained by the relativistic modification of the model.Finally,the Cornell potential and KMS potential used in this paper are briefly introduced.In the third part,we discuss in detail the mode of giving the spatial wave function of N=3 harmonic oscillator shell and the construction of harmonic oscillator configuration satisfying SU(6)symmetry.In the fourth part,the Cornell potential and KMS potential are applied to the model given in the second part.