A Study Of The Qqqs(?) System Under The Chiral Quark Model

With the continuous development of experimental technology,many exotic states have been discovered in experiments in addition to traditional baryons and mesons.For example,in 2003,the pentaquark state ?+ was observed by LEPS Collaboration.However,with the improved experiments with higher accuracy,the existence of the state was denied.But the work of exploring pentaquark has started,and we will not stop to study.In fact,to explain the problem "mass inversion" of the excited baryons,researchers put forward a series of different opinions.The most popular one is that these states contain pentaquark components,such as N*(1440)?N*(1535)and A*(1405).The pentaquark components contained in N*(1440)may be uudqq,q=u.d,the pentaquark components of N*(1535)state can be uduss and the pentaquark components in A*(1405)state is udsqq,q=u,d.?*(1405)is what we mainly explore in this paper.To explain this exotic state,some theorists believe that its main component is NK,while some scholars believe that the main contribution comes from the ?? state.Based on this question,we will investigate the pentaquark system qqqsq,q=u,d based on the chiral quark model.The numerical method used is the Gaussian expansion method,which is the one with high precision in few-body problem.First,we calculated the baryon and the meson spectrums.Since the same set of parameters cannot describe them well simultaneously,Therefore,in order to check the dependence of our model on parameters,two sets of parameters are employed to calculate the hadron spectra.In this work,two different structures are involved:qqq—sq and qqs—qq.The final calculation results show that the ?? and NK states with quantum numbers IJP=01/2-are bound,and finally by coupling all channels of the system we can also obtain an eigen-energy close to ?*(1405).The corresponding eigen-state has larger components of NK,so we tend to interpret it as the NK state.In the system with quantum numbers IJP=03/2-,there is indeed a resonance state whose energy is very close to the A*(1520)which experimentally found.However,due to the large decay width of its main component ?*?,we cannot interpret it as ?*(1520).Finally In the system of IJP=05/2-,we get a resonance state with energy in the range of 2156?2158 MeV,the decay channel is ?*?????? with the decay width around 185 MeV.For the system of I=1,only ?K and ?K*have a certain binding energy,however,after coupling all the entire system respectively there is no resonance states coming out.Finally,for the entire I=2 system,there is nether bound state nor resonance state appearing.So far,our calculation for baryon,mesons and pentaquark states are limited to the ground state,all the orbital angular momenta are set to 0.The work on excited states have not been calculated yet,which requires further research.The three-quark states and five-quark states will be mixed up if they have the same quantum numbers,these coupling is also needed to be considered.