Calculation Exotic Meson Spectrum And Coupled Channel Effects

In the traditional constituent quark model, the meson is consisted of quark-antiquark, the baryon is composed of three quarks. By considering the chiral symmetry spontaneous breaking of the quantum chromodynamics, the fundamental theory of strong interaction, the current turns to constituent quark, the quark-quark interaction can be resumed as follow, color confinement potential, one-gluon-exchange potential and Goldstone-boson exchanges potential. Constituent quark model is successful in describing the properties of hadron: hadron spectroscopy, the decay of hadron and the hadron-hadron interaction etc. But there are some problems remained, for example, baryon N(1440), Λ(1405), meson f0(600), κ(800) and so on cannot be explained in the model. It’s also difficult to find the place of the new states Y(2170), X(3872), Y(4160) etc.("XYZ" particles), which are reported by experimental groups recently, in the constituent quark model. So it is very interesting to study the properties of these particles. Possible explanations for these particles have been proposed, molecular state. Multi-quark state, hybrids etc.Theoretically, the meson is composed of quark-antiquark. the baryon is consisted of three quarks. In fact, there are multi-quark and gluon components,|Baryon)=C0|qqq)+C1|qq>+C2|q3g)+C3|q3(qq)2)+|Meson>=C0|qq)+Cc|qqqq)+C2|qqg>+C3|qq(qq)2)+….(0-2)In the constituent quark model, we assume that the high Fock component, multi-quark and gluon components can be absorbed by the parameter in the model. It is expected to be a good approximation for the low hadron spectroscopy, the model can well describe the experimental data. However, the approximation may not work for the highly excited states, especially the highly excited states may decay into two hadrons. So we should think about the contribution of high Fock components. The recent calculation of charmonium spectrum has inferred this.The present work is to consider the contribution of four quark components in calculating hidden-strange quarkonium spectroscopy, and to fit the experimental data of.ss spectroscopy by adjusting parameter and to check whether the high Fock components can be absorbed by the parameters or not. As an preliminary work, the four quark component is restrained into two colorless clusters, that is to say the original quark and antiquark will combine with the antiquark and quark excited from the vacuum to form two ground state mesons. The excited states of the created mesons and the hidden color channels (two colorful clusters forming colorless four-quark states) are not taken into consideration. Considering the effect the four quark component in meson spectroscopy is referred to as the channel-coupling effect. Under the non-relativistic theory frame, the particle number is constant, the two-quark composition will not mix with the four-quark composition, so coupling effect is a kind of relativistic effect.In the study of the channel-coupling effect, the3P0model (quark pair creation model) is used. The model has given a successful description of the strong decay of hadrons. Our calculation show that the four-quark components has a rather large effect on the ss spectrum, especially for the highly excited states. And the effect of four-quark components cannot be absorbed by adjusting the model parameters. By analyzing the components in the states, the quark-antiquark component is still the major component. But for some states, the percent of the four-quark components is about30%. In the present calculation, the four-quark components are restricted to be two colorless ground state mesons. The contributions from the hidden-color channels and the excited states of mesons worth to be studied to check the convergence of the model.In addition, the mass shifts for SU(2) vacuum (which only u,d-quark pairs are excited from the vacuum) are compared with that for SU(3) vacuum (u, d, s-quark pair are excited from the vacuum). We found that the mass shifts of the latter are smaller than that of the former. The reason is that the smaller vacuum excitation strength are used.γs=γ/√3, which is due to the larger s-quark mass.The most time-consuming part of the work is to adjust the parameters to fit the experi-mental data. In the present work, the readjusted parameters are:quark masses, confinement strength, the quark-gluon coupling constant, other parameters are kept unchanged. By fit-ting the experimental data, one set of parameters are choose to re-calculate the ss spectrum. By considering more four-quark components and readjusting all the model parameters to fit the experimental data is the next work of our group.