With The Qcd Model To Study The Four-quark Systems

During the last few years,the B factory successive report Tetraquark States existence of signal.All of them have stimulated a renewed interest in the discovery,of Tetraquark States.In 2003 BABAR Collaboration at SALC announced a positive- parity narrow state with a rather low mass 2317±3MeV in the D_S⁺(1969)Ï€channel with total widthΓ＜7Mev,which was confirmed by CLEO later.Because of its low mass and decay angular distribution,its J^P is believed to be 0⁺.In the same experiment CLEO observed a state at 2457 MeV with a possible spin-parity J^P = 1⁺ in the D^*Ï€channel with total widthΓ＜7Mev.Later,both the two states were confirmed by BELLE.In addition,BELLE announced a state with mass 3872Mev.In 2005 BABAR Collaboration reported the discovery of Y(4260)with total widthΓabout 50 90Mev.In addition,the experiment also reported several other possible Tetraquark just likeσ(600),a₀(980),f₀(980).Theoretially,almost every quark model,nonperturbative method,includeing lattice QCD,have not been able to give a conclusive compellent answer.Quantum chromodynamics(QCD)is generally accepted as the fundamental theory of the strong interaction.Because of the asymptotic freedom,the perturbation method can be applied,high-energy phenomena can be described very well by using its fundamental degrees of freedom,quarks and gluons.However.the direct use of QCD to low-energy phenomena: hadron-hadron interactions and multi-quark systems,is still impossible because of the nonperturbative properties and the complications of QCD.So at present and even in the future, the QCD-inspired model will be a useful tool to explore the secret of strong interaction systems,especially the multi-quark systems,which have abundant color structures.The research of multi-quark system may play an important role in understanding the low-energy behavior of QCD.The most commonly used quark models are the constituent quark models, and the chiral quark model is one of them.With the help of several adjustable parameters, the existed experimental data on meson and baryon properties and hadron-hadron interactions can be fitted well in model.It is very difficult to discriminate among most models by using the existed experimental data,even the newest ones.Clearly the more are the parame- ters,the poorer is the capability to predict.To solve this problem,each model must carry out more calculations to explain the updated experiment data.At the same time we must locate some phenomena which depend on model sensitively.Multi-quark system may be a good place for this purpose,recent calculations by various models have shown that.To describe hadron-hadron interaction,σmeson is indispensable in various quark models.However the existence ofσmeson is still in controversial.Recently there are some progress,the signals ofσmeson are revealed,but the "discovered"σmeson which is identified as S-wave resonance of twoÏ€'s,can not introduce enough attraction in nucleon-nucleon(NN)interaction. Is there an alternative approach to the intermediate range attraction of NN interaction? It is an interesting problem.QCD tells us that the interaction between quarks is generally a multi-body interaction.The two-body approximation is proved as a good one in the hadron properties.However the validity of the generalization to multi-quark system is still an open question.The quark delocalization color screening model(QDCSM)was developed in 1990s on the basis of conventional constituent quark model by F.Wang et al.Applying to hadron, it is just the Glashow-Isgur model,which the hadron properties can be described well.Applying to NN interaction,the intermediate range attraction can be obtained withoutσmeson. The model takes into consideration of multi-body interaction among quarks,and assumes the q-q interaction depends on the states quark occupied.The screened color confinement is introduced to imitate the coupling effect of the various color structures.The main advantage of QDCSM is that it allows the multi-quark system to choose its most favorable configuration (by variation the energy of the system to delocalization parameter)through its own dynamics.The model has few parameters and therefore has strong prediction power.It has been applied to the study of baryon-baryon interactions(deuteron properties,N-N,NA, NΣ,etc.)and a good agreement with experimental data-is obtained.Applying to dibaryon, several interesting dibaryon candidates are obtained.Foregoing checking shows that theσmeson effect can be replaced by quark delocalization and color screening mechanism,which can obtain the intermediate range attraction.But the long-part interaction is missing by QDSCM.QDSCM was extended by including pseudoscalar meson exchange(Goldstone-boson-exchange)to account for the long-range part of the baryon-baryon interaction,which we were missing before.The extended QDCSM has been applied to the study of baryon-baryon interactions(deuteron properties,D-wave mix,NN etc.)and a good agreement with experimental data is obtained,and a good agreement with experimental data is obtained.The extended QDCSM includes the screened color confinement potential,one gluon exchange potential,and pseudo-scalar(Ï€,Κ,η)meson exchange potential.This work presents the results of a systematic search of possible tetraquark states in the framework of extended QDSCM.We search of possible tetraquark states with the help of adiabatic approximation,then we study the interested states by dynamics technique.For the heavy quark system,the results show that mostly states have attractive potential. Although our results drive down by quark delocalization and color screening mechanism,it is not high enough to be resonance.For other states just like c(?)n(?),c(?)s(?)and c(?)n(?)/c(?)s(?)which is interested by many people,also we get the results driving down by quark delocalization and color screening mechanism,at the same time them can be resonance,though resonance energy is higher than experiment.Dose the pentaquark really exist? More and elaborate experiments and academic study are needed to clarify the situation.