A Study On The Four-quark Chiral Quark Model With Heavy Flavor

Since 2003,many exotic hadrons called XYZ particles have been discovered exper-imentally,which has led to extensive research.In 2015,the LHCb team reported two five-quart states with cc;In 2016,researchers at the Fermi Lab DO team found the state X(5568),which is considered to contain four different quark flavors u s d b,where c,b are heavy quarks.Raise the upsurge of research,testing and prediction about the states contain heavy quarks in physics.Due to the lack of experimental evidence related to the interaction between the two heavy quarks,whether a four-quark state,which contains two heavy quarks QQ and two light anti-quarks qq,is stable or not has been unknown.In September 2017,the LHCb Collaboration released a discovery of the doubly charmed baryon ECC was found to be the key experimental evidence for the final reso-lution of this issue.They collided with the proton-proton of the 13Tev centroid energy and found an important structure in the invariant mass spectrum of ?c+K-?+?+.They determined that it is the baryon Ecc++,the composition is ccu,and the quality is 3621.40±0.78MeV.The discovery of(?)cc++ confirms some of the theoretical predictions that fill the gap between the experimental basis of experimental evidence related to the interaction between QQ,indicating that there is a reliable starting point for the study of systems containing two heavy quarks.Naturally,more attention has been paid to the use of theoretical models and computational methods to study and predict tetraquark states with multiple heavy quarks,for example bbud,bcud,ccud,etc.In theoretical calculations,QCD is a standard dynamics theory describing the strong interaction of quark-gluons.Various non-perturbation theories are also evolving,and the phenomenological quark model has been successful in describing the properties of hadrons.The work of this paper is based on the phenomenological quark model,using the chiral constituent quark model,Gauss expansion and other methods with higher precision,to study the four quark states with multiple heavy tastes from the perspective of the four-body system.This article will focus on the following work:The first part is the introduction of quark models and calculation methods.Tradi-tional theory holds that hadrons are divided into baryons and mesons,and the nature of them is not mysterious.But,there is no theoretical rule prohibiting more quarks or anti-quarks from forming singular hadrons,like a four-quark particle consisting of two quarks and two antiquarks and a five quark particle consisting of four quarks and one antiquark.There are many viewpoints and models on the structure of exotic states,and the chiral constituent quark model is the model adopted in this paper.Using Gauss expansion and the infnitesimally-shifted Gaussian basis functions(ISG)can solve the energy of exotic states more rigorously,and improve the credibility of calculation results.In the second part,the meson spectrum is calculated using the chiral constituent quark model.In order to check the parameter correlation of the model results,we selected 3 sets of parameters to calculate the energy spectrum of the meson.Comparing the results,we found that the energy spectrum calculated agrees well with the experimental values.The third part mainly studies bcud(J~P=0~+).Under the framework of the chiral constituent quark model,we used the multi-Gaussian expansion method and select 3 sets of parameters to perform accurate four-body dynamics calculations.In the calculation process we consider both the meson-meson and the diquark-antidiquark structure,all possible color structures and couplings.We also take the spin configuration and the coupling of all possible channels into consideration,from the perspective of the equivalent potential,the dynamics calculation and the distance between quarks.The results show that the bcud(I=0)system may have 2 bound states.One is the compact four-quark state,with an energy of about 6922?7020 MeV,and the other is molecula.r states with an energy of about 7100?7150 MeV.And the qualitative results of the 3 parameters are consistent,indicating that bcudJP=0+state does not depend on parameter selection-It is a good candidate for a four quark state and deserves further study.With the emergence of more exotic states,the research on multi-quark states will deepen our understanding of the basic theory of strong interactions.The constituent quark model has achieved great success in explaining the hadron spectrum and the hadron-hadron interaction,but there are still deficiencies in the multi-quark state.It is hoped that through this work,we will enhance our understanding of quark models,promote further improvement of them,and make more predictions of new states.