Quark Model Studies D_s0^* (2317) And X₀ (2900)

In 2003,the Belle collaboration discovered charmonium state X(3872),and this exotic state was confirmed by other groups.In the same year,the Bar Bar collaboration and CLEO collaboration found the D_s0^*(2317)and D_s1(2460)states in the invariant mass spectrum D_s⁺?⁰and D_s^*+?⁰,respetively.In the following decades,a large number of exotic states have been reported,which aroused the interest of physicists in searching for multiquark hadron states.With regard to D_s0^*(2317)and D_s1(2460),people use various methods to study their properties such as mass,quantum number,decay width and structure.Besides these two states,many similar charmoium-like exotic state with c(?) meson have been found in many experimental groups.But so far,their internal structures have not been fully understood.At present,there are mainly the following explanations:the molecular state structure of DK,the traditional c(?) meson,the mixed state of the meson and the tetraquark,and so on.Last year,LHCb group discovered two new exotic states X₀(2900)and X₁(2900)in the process of B⁺?D⁺D^-K⁺,and their smallest quark composition is ud(?)(?).The flavor of the tetraquark is different,which means that these two states are all tetraquark states.A large number of theoretical studies have been put forward to explain these two exotic states,including molecular state structure,compact tetraquark state,diquark-antidiquark structure,and mixed state of molecular state structure and diquark-antidiquark structure.For strong interaction systems,the Quantum Chromodynamics(QCD)theory is gen-erally regarded as the basic theory for studying strong interaction.The theory can solve the problem of hadron properties by perturbation theory in high energy region.But the low energy hadron physics belongs to the non-perturbation problem of QCD and how to solve the low energy non-perturbation QCD is a major problem in contemporary physic-s.In recent years,the lattice QCD theory,Dyson-Schwinger equation,effective field theory method,and QCD sum rules have made important progress in the study of the ground state hadron physics,but they are still difficult to deal with the excited states and scattering states.The phenomenological quark model based on the theory of QCD is an-other effective method to study hadron-hadron interaction.It can describe the properties of ground state baryon spectrum,meson spectrum,hadron-hadron interaction,deuteron and so on.One of the most widely used models is the chiral quark model,which is char-acterized by the medium range attraction provided by the?-meson exchange.However,whether the?meson exists or not has not been determined.Another quark model is the quark delocalization color screening model(QDCSM),which provides the medium range attraction of hadron-hadron interaction by introducing color screening factor and quark delocalization effect.The model can not only describe the ground state of baryon spectrum and meson spectrum,nucleon-nucleon interaction and deuteron properties,but also predict some dibaryon states,such as d^*,N?and so on.Great success has also been achieved by this model in the recent discovery of the hidden charm pentaquarks.Therefore,in this work,we extend the QDCSM to the study of the tetraquark system.In this paper,we focus on the study of D_s0^*(2317)and X₀(2900)in the framework of the QDCSM.We systematically studies these two tetraquark systems:cq(?)(?) and qq(?)(?).Both the resonance group method(RGM)and the generating coordinate method(GCM)are used.We consider two kinds of structures:the meson-meson structure and the diquark-antidiquark structure,and the interaction potential between two clusters is also studied to judge whether there is a resonant state.In addition,we not only study each single channel,but also do the multi-channel coupling calculation,so as to study the multi-channel coupling effect.The results are as follows.(1)There is no bound state in the tetraquark system with the composition of cq(?)(?).So the D_s0(2317)can not be interpreted as DK molecular state in our current model framework.The study of the effective potential in the diquark-antidiquark structure shows that it is possible to form some color-structure resonance state,and the resonance energy is about 2580?3100 MeV.This needs to be further determined by scattering resonance calculation.Moreover,we extend our work to the tetraquark system with bottom quark bq(?)(?),and obtain similar results to the system cq(?)(?).There is no bound state in the system of bq(?)(?),so it is impossible to obtain the X(5568),which is reported by the experimental group D0.In the diquark-antidiquark structure,we calculate that the energies of the quantum numbers IJ^P=00⁺and IJ^P=01⁺are 6032.7 MeV and 6056.4 MeV respectively,which are consistent with the experimental results that the energy of is very close to the one of the excited states of B_s⁰,which may be a resonant state,which needs to be studied by scattering resonance in the future.(2)In the tetraquark system with the composition of qq(?)(?),we have obtained a molec-ular state of(?)^*K^*with the quantum number of IJ^P=00⁺and the single channel energy is 2820.7 MeV,which is lower than the theoretical threshold of(?)^*K^*and can be used to interpret the X₀(2900)state.We are also trying to consider the effect of instanton exchange interaction to the X₀(2900)state.The result is consistent with the one of the QDCSM,which shows that both two models support to explain the X₀(2900)as the molecular state of(?)^*K^*with the quantum number of IJ^P=00⁺.After the calculation of the channel-coupling,we also get two bound states:the quantum number are IJ^P=00⁺and IJ^P=01⁺and the energies are 2341.2MeV and 2489.7 MeV,respectively.The study of the interaction potential between diquarks and antidiquarks also shows that there may be color structure resonances with the energy range of 2500?3100 MeV.In the same way,we extend our work to the four quark system with bottom quark qq(?)(?),and obtain similar results to the system qq(?)(?).The molecular states of B^*K^*with quantum number of IJ^P=00⁺are obtained in the system of qq(?)(?),The energy is about 6147.2 MeV.After multi-channel coupling calculation,we obtain two bound states,one of which has a quan-tum number of IJ^P=00⁺,and an energy of 5757.8 MeV,The other quantum number is IJ^P=00⁺,and the energy is 5798.0 MeV.All these are our preliminary work on the tetraquark system.We need to further couple the meson-meson structure and the diquark-antidiquark structure to calculate the scattering process of the open channels and find the teraquark resonance.In addition,we will use the unquenched quark model to consider the coupling calculation of the quark-antiquark state and the tetraquark state,and further study the charmoium-like exotic state containing c(?),analyze their composition and structure,explain the experimental data,and provide more theoretical information for the experiment.