Quenched Quark Model Interpretation And Non-quenched Quark Model Interpretation Of Exotic States

Although quantum chromodynamics（QCD）can help us better understand strong in-teraction,QCD belongs to non-perturbative problem.It’s difficult to solve problem from first principle of QCD.Although the lattice QCD develops rapidly,we have to take advan-tage of phenomenological model to better study QCD due to the shortcoming of lattice QCD.Of all of phenomenological model,quark model is a most successful model,because it not only explain data from experiment but also predicts the existence of new particles,such asΩand d^*.For explaining the newly XYZ particles from a theoretical point of view,this paper will extend the traditional constituent quark model to multi-quark quark model and add rich color structures and space structures.If taking hadron loop effect into consideration,some exotic particles may be a mixture of two quarks and tetra-quark.Consequently,we develop unquenched quark model（3P0 model）.In this way,the newly XYZ particles can be well describe.This paper is listed by the following parts.In 2016,（?）_ccwas found by LHCb and X（5568）was reported by D0 indicate that the hadron with two heavy quarks may exist.This paper calculates tetraquark system（QQ（?）,Q=b,c,s）with two heavy quarks in the frame of both molecular structure and diquark-antiquark structure.Due to limit of symmetry,QQ（?）,Q=b,c,s system only has one kind of IJ^P=01⁺,while QQ′（?）,Q=b,c,s has three kinds of IJ^P,00⁺,01⁺and02⁺。For 01⁺QQ（?） system,if Q=b,the BB^*,the lowest energy channel,is a bound state,and the diquark channel,6（?）（?）,is deeper bound state;if Q=c,none of molecular channel is a bound state,while the diquark channel,6（?）（?）,is deeper bound state;if Q=s,every physical channels is scattering state.In a word,with the mass of heavy quark become lower,the 01⁺QQ（?） system will be hard to have bound states.On the other hand,similar to 01⁺QQ（?） system,if bc（?）,the diquark structure of IJ^P=00⁺,01⁺,02⁺QQ′（?） system is a bound state.While the s quark is added into IJ^P=00⁺,01⁺,02⁺QQ′（?） system,every physical channel is unbound.For better understanding hadrons with two heavy quarks,we couple two structures include both molecular structure and diquark-antiquark structure and find the bound states exist in every possible systems.For example,before coupling structures,the lowest eigen-value of 01⁺bb（?） system has 200 MeV bound energy and the lowest eigen-value of 01⁺ss（?） system is a scattering state.After coupling structures,the lowest eigen-value of 01⁺bb（?） system has nearly 300 MeV bound energy and lowest eigen-value of 01⁺ss（?） system is swallower bound state.In 2019,Belle Collaboration reported a new particle,Y（4626）M=4625.9_-6.0^+6.2±0.4MeVΓ=49.8_-11.5^+13.9±4.02)±0.4MeV,in D_sD_s1（2536）invariant mass spectrum.It’s decay mode(D_sD_s1（2536）)indicates that the Y（4626）should include charm quark and strange quark.In addition,the belle Collaboration suggest the IJ^Pof Y（4626）is 01^-.Due to the mass of Y（4626）very close to D_sD_s1（2536）,by means of Guass-expand method,a accurate few body calculation method,we use tetraquark picture to describe Y（4626）.After coupling different structures,we got redundant energy levels.For examining the stabilities of these energy levels,we take advantage of real-scaling method and got a stable state,R（4531）.Similar to Y（4626）,in 2019,LHCb Collaboration reported X（2900）with 5σin D^*K^*invariant spectrum.However,the LHCb Collaboration didn’t give information about Parity.Base on coupling channels and real-scaling method,we got several stable resonances,R₀（2904）Γ=41.8MeV,R₁（2906）Γ=29.1MeV和R₁（2912）Γ=10.2MeV.We suggest the R₀（2904）with positive parity may be a good candidate of X₀（2900）,so X₀（2900）may enjoy positive parity.On the other hand,because the width of the R₁（2912）and R₁（2906）are incompatible with X₁（2900）,we can’t determine the parity of X₁（2900）.The famous X（3872）has always been a controversial state,and there is no clear con-clusion until now.From the energy point of view,the mass of X（3872）is dozens of Mev lower than the energy predicted by the traditional quark model,but it is very close to the threshold of DD^*.Therefore,many people think that X（3872）may be a molecular state,but the attractive force from exchange ofπis too weak to bound the DD^*system.From an experimental point of view,BaBar’s（?）=3.4±1.4 supports X（3872）is the traditional two-quark state,while Belle’s （?）=1.0±0.4±0.3 implies that X（3872）is a four-quark structure.Neither the peculiar four-quark explanation nor the traditional two-quark explanation is convincing.In order to better describe the ex-periment,we assume that the meson has both two-quark and four-quark components,|M>=C₁|q（?）>+C₂|q（?）q（?）>.We hope that through the unquenched quark model,we can uniformly describe all the mesons found in the experiment,so as to get a convincing explanation about X（3872）.We found that the traditional non-quenched quark model（3P0 model）has some unreasonable problems.Therefore,before calculating X（3872）,our first step is to propose two correction factors through the calculation of the light media system.,The traditional T operator has been modified reasonably.In the second step,we apply the revised T operator to the calculation of X（3872）.After calculation,the re-sult shows that X（3872）is a mixed states with 70%c（?）.Similar to X（3872）,the D_s（2317）discovered in 2003 cannot be explained well by theory and experiment too.Using the modified non-quenched quark model,we fitted the D_senergy spectrum,and obtained almost a mixed states with two quarks and four quarks each accounting for half.The quark model is a good phenomenological model when it was used to explain traditional hadron in the past years.Recently,with the development of experiment,more and more exotic states are reported,so the traditional quark model has to extend to multi-quark model.We hope the unquenched quark can unify both traditional hadrons and exotic hadrons,which can help us better understand QCD and hadron physics.