Qdcsm And Pentaquark Model Study

Quantum chromodynamics (QCD) is generally accepted as the fundamental theory of the strong interaction. High energy processes are calculable using perturbation method due to the asymptotic free property of QCD, however, owing to the infrared confinement, low and middle energy strong interaction systems can not be resolved directly in QCD. At present and even in the future, the QCD-inspired model will be a useful tool to explore the secret of strong interaction systems. The often used quark models are: bag model, soliton model and potential model, etc. Potential model is the most convenient and used most model in hadron-hadron interaction and multi-quark system. There are also several version of potential model according to the degree of freedom used, they are: meson-exchange model, one-gluon-exchange model and hybrid model. All of these models are successful for the meson and baryon properties. Because any small disagreements with the experiment data can generally be repaired by many fine-tuning parameters, it is very difficult to discriminate among most models by using the existed experimental data, even the newest ones. Clearly the more are the parameters, 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 have shown that. More important we can also obtain more information about low energy QCD through studying multi-quark system.In this work, we study the pentaquark state (?)⁺, which was "discovered" recently inexperiments, in the framework of quark delocalization color screening model (QDCSM). QDCSM was developed in 90s of 20^th century on the basis of conventional potential model, which amends orbital wave function to enlarge the model space and amends the confinement potential to take into consideration of the interactions between quarks depends on their states. The model has few parameters and therefore has strong prediction power. The model has been applied to the study of baryon-baryon interactions (NN, NA, N∑, etc.) and agreement with experimental data is obtained. Applying to dibaryon, several interesting dibaryon candidates are obtained.(?)⁺ is an exotic baryon which was discovered in reaction γn → K⁺K^-n by LEPS in 2003. It has baryon number 1, strangeness +1, spin 1/2, isospin 0 and mass 1540MeV. It decays into K⁺n or K⁰p with width less than 25MeV. (?)⁺ has smallest quark content uudd(s|ˉ) according to its quantum numbers. The discovery was confirmed subsequently byseveral groups. However, some groups claim that they don't find ?+ 's signal. In theory, allkinds of models, including lattice QCD, are applied to the study of 0+. Different color and spacial structures have proposed and results with large difference are obtained. In this work, we carry out calculations about the mass of ?+ with different color and spacialconfigurations using adiabatic approximation in QDCSM. The mass of ?+ with KNmolecular state is 1615 MeV, channel coupling calculation gives us the same result. Both Jaffe-Wilczek's diquark model and Kaliner-Lipkin's Diquark-triquark model have the mass1780MeV and 1653MeV respectively. Diamond 0+ has single channel mass of 1594MeV, channel coupling reduces the mass to 1523 MeV. In the case of NKk model, effective potential of system is -90MeV. More reliable estimate of 0+ mass can only be obtained byinvoking dynamical calculation. Except 0+ with diamond structure is close toexperimental value, others are higher. Does 0+ really exist? What are the spin and parity?More and elaborate experiments are needed to clarify the situation. In addition, multi-quark system has abundant color structures than ordinary hadrons, how do those color structures interplay, which is an open question deserving further investigation.