The Study Of Charmonium Spectrum In Chiral Quark Model

Recently, some new kinds of resonance states characterized by their charmed de-cay products have been reported by Belle, Babar and other collaborations. These XYZ states has aroused intensive interests for theoretical and experimental physicists.Possible explanations for these particles have been proposed, charmonium, gluon ball, tetraquark, molecular state and hybrid etc.According to the conventional traditional quark potential models that a meson is composed of two naive quarks, some of the states can be fitted well while most of them cannot be fitted well. In fact, there are also some high Fock components, qqqq, qqqqqq, qqg, …, in the meson. By means of the duality of quark and hadron, the effects of the high Fock components can be represented by the channel-coupling between charmonium and DD-meson channels. It is also called coupled channel effect. But It is still an open question wether this effect can be negligible or not. The effect is studied by calculating the charmonium spectrum at present. In this work, only four-quark components are taken into account and the four-quark components are limited to two singlet mesons and the bound state part of the four-quark components are neglected.Therefore, the following topics are studied in this paper.1. The quantum chromodynamics (QCD) is believed to be the fundamental theory of the strong interaction theory. And the phenomenal constituent quark models have the properties of QCD and achieve a great success in mid-and low-energy experiments. Some experiments and the possible explanations about charmonium and XYZ particles are reviewed.2. Some light mesons. D(D) mesons, DS(DS) mesons and charmonium spectrum are calculated with the Gaussian Expand Method (GEM) under the phenomenological con-stituent quark model. Furthermore, the orbit wave functions of mesons in the momentum space are given out.3. The open flavor strong decay widths and some branching ratio of χcJ(nP) (J= 0,1,2), (n=1,2,3) and ηc(ns) (n=3,…，6) are calculated under the 3Po models. And the possible explanations of X(3872)、 X(3915)、X(3930)、X(3940)、X(4140) and X(4160) are discussed.4. The mass shift caused by the high Fock components and the influence on the open flavor two-body strong decay of the mass shift are calculated by considering the nonrelativistic coupling effect.So the following results are obtained.1. The theoretical masses of χcJ(1P)(J= 0,1,2),χc2(2P),ηc(1s) and ηc(2s) are consisted with the experimental data. But χcJ(nP) (J= 0,1.2,n≥ 2) and ηc(ns) (n= 3,…,6) are still not so clear in theory and experiments.2. The decay width of χc2(2P) is consistent with the experimental data of X(3930). so the assignment of X(3930) as λc2(2P) is supported by the model. The decay width of χc1(2P) is sensitive to its mass. However, if the channel coupling effects shift ist mass to 3872 McV, its decay width will be around 1 McV. The possibility of assigning the state X(3872) as χc1(2P) cannot be excluded. To assign X(3915) as χc0(2P) is disfavored, due to the unmatching of decay channel.The possible candidates of χc0(3F) are X(4160) and X(4140). Their masses are close to the theoretical ones. The experimental branching ratio of X(4160), Γ(X(4160)�'D-D)/Γ(X(4160)�'D$D.< 0.09 is compatible with that of χc0(3P),0.07. However the broad decay width of X(4160) cannot be explained by the open charm two-body decay. To assign X(4140) as χc0(3P) is also possible, due to the compatibility of the total decay width.3.The explanation of X(3940) as ηc(3S) is possible because the decay width of ηc(3S) is in the range of the experimental value of X(3940). Although the mass of X(4160) is about 110 MeV less than that of ηc(4S) and the decay width of X(4160) is much larger than that of ηc(45), the assignment of X(4160) as ηc(4S) cannot be excluded due to the large uncertainty of the experimental decay width and the compatibility of the branching ratios of ηc(4S) with that of X(4160), and the mass of ηc(4S) can be shifted downwards by taking into account the coupling effect of the open charm channels.4. The mass shift can suppress the mass of mesons significantly and cause much influence on the decay width.The chiral constituent quark models achieve a great success on hadron physics, but there are still some unsolved problems. With the discovery of new hadron states and as the research goes further, the development of the quark model is needed. By considering the coupling effect and the mixing of diquark and tetraquark, it is possible to solve the problems in new hadron states. And it is expected to offer some help to understand and predict some new hadron states. Further experimental and theoretical work will deep our understanding of hadron physics and QCD.