Non-Strange Six-Quark States And The Structure Of Z_c Particle In A Chiral Quark Model

So far, all of the observed hadrons can be classified into two types, baryons composed of qqq and mesons composed of qq. But in principle, the QCD fundamental theory does not exclude the existence of the multi-quark states containing more than three quarks, such as tetraquark, pentaquark, dibaryon, hexaquark, et al. The structure of such kind of multi-quark states is completely different from the traditional baryons and mesons. They will definitely provide us more valuable information about the strong interaction and the structure of hadron. Moreover, whether those multi-quark states do exist or not could help us to test various phenomenological models and even the QCD fundamental theory itself. Actually, the structures and properties of multi-quark states have always been international hot topics in the area of hadron physics.Due to the non-perturbative behavior of QCD in low energy region, people still need QCD-inspired models to help in the study of hadron physics. Among these models, the chiral SU(3) quark model and the extended chiral SU(3)) quark model are quite successful in reproducing the energies of the hadron ground states, the hadron-hadron scattering phase shifts and cross sections. Inspired by these successes, we in this thesis continue to apply these two models to study the non-stranged six quark states and the structure of the Zc particle.Some interesting results are obtained:· The wave fuctions of various configurations of the non-stranged six quark system are constructed by using the group theory techniques, and their energies are calculated in the extended chiral SU(3) quark model. The results show that only the I(JP)=0(3+) state is lower than the threshold of the corresponding two comparable baryons by use of the reasonable parameters, and it could exist as a possible hexaquark state.· 12 configurations of the S-wave udcc system are constructed by using the group theory techniques, and their energies are calculated in both the chiral SU(3) quark model and the extended chiral SU(3) quark model. The results show that by use of the reasonable parameters the positive charged states Zc(4020) and Zc(4025) can be interpreted as possible udcc tetraquark states with quantum numbers I(JP)=1(0+) or I(JP）=1(1+）. However, Zc(3900) is difficult to reproduce its observed low mass of the by use of the reasonable parameters. We conclude that the Zc(3900) is difficult to be interpreted as tetraquark state.