Study Of Multi-Quark Systems In A Chiral Quark Model

The study of the properties of hadrons and exotic states as well as the hadron-hadron interactions on quark level are the important tasks in the strong interaction physics. It is a general consensus that QCD is the underlying theory of the strong interaction. However, since there is no serious practical approach to deal with the non-perturbative QCD effects which are important for the light quark systems in low energy region, people still need various QCD-inspired models to help. Among these models, the chiral SU(3) quark model and the extended chiral SU(3) quark model have obtained quite success in reproducing the energies of the baryon ground states, the binding energy of deuteron, the nucleon-nucleon phase shifts, and the nucleon-hyperon cross sections, and also have got some developments in the study of the baryon-meson interactions, e.g. KN,ΛK,ΣK,ΔK, and Nφ. In this thesis, we study the structure of the low-lying uds|-s|- state and the properties of some other baryon-meson interactions. Some interesting results are obtained:The energies of the low-lying isoscalar and isovector uds|-s|- configurations with spin-parity J^P = 0⁺, 1⁺, and 2⁺ are calculated in the chiral SU(3) quark model and the extended chiral SU(3) quark model by use of the varia-tional method. The contributions of various parts of the interacting potentials including the s-channel interaction are investigated, and the effect of different forms of confinement potential is examined. The model parameters we used here can satisfactorily describe the energies of the baryon ground state, the nucleon-nucleon scattering phase shifts and the hyperon-nucleon cross sections. The parameters of the s-channel interaction are fixed by the masses of K and K^* mesons, for which the size parameter is taken to be two possible values. When it is chosen as the same as baryons', the numerical results show that the masses of all the uds|-s|- configurations are higher than the corresponding meson-meson thresholds. But when the size parameter for the mesons is adjusted to be smaller than that for the baryons, the uds|-s|-configuration with I = 0 and J^P = 1⁺ is found to lie lower than the K^*K^* threshold, furthermore, this state has a very small KK^* component and the interaction matrix elements between this state and KK^* is comparatively small, thus its coupling to the KK^* channel will consequently be weak and it might be regarded as a possible tetraquark candidate.The structure ofΩ_Ï€,Ω_ωandΩ_ρstates are dynamically studied in both the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving a resonating group method (RGM) equation. The calculated results show that in these systems theσfield provides the attractive interaction, and in the extended chiral SU(3) quark model such an attraction can make forΩ_Ï€,Ω_ωandΩ_ρquasi-bound states with the binding energies of about several MeV. Especially, bothΩandÏ€have the traits of long life [in order of 10^-10 and 10^-8 seconds], and there is no coupling channel below the threshold ofΩ_Ï€, thus its width must be narrow. Furthermore, theΩ_Ï€^-state might be easily distinguished and detected in the experiments since it has two negative electronic charges. We call for experimentalists to search for this interestingΩ_Ï€state in the e⁺e^- collisions or heavy ion collisions.