Non-strange Light Hexaquark In The Constituent Quark Model

Hadron spectrum is an important routine to recognize the internal structure and dynamics of hadron,and is also one of the hot topics in hadron physics.Based on the study of the hadron production,one has recognized that hadron is a bound states made of quarks via strong interactions,while quantum chromodynamics(QCD)is the basic theory for describing strong interactions.QCD has three basic characteristics:asymptotic freedom,color confinement,and chiral symmetry breaking.Because of the asymptotic freedom characteristics of QCD in the high energy region,the perturbation method is applicable for the high energy processes.However,in the low energy region,QCD is highly nonperturbative,and hence the nonpertabative method has to be develop to treat the low energy processes.Now,various non-perturbative QCD methods have been proposed,such as lattice gauge theory(LQCD),QCD sum rules and constituent quark model.The LQCD and QCD sum rules have practical computational difficulties and can only treat ground states.The QCD-inspired constituent quark models are easy to compute,and more importantly can not only calculate the hadron ground states but also the excited states,so the constituent quark model is widely used to treat with the low-energy hadron systems.Theoretically,QCD do not rule out the existence of multiquark states such as tetraquark,pentaquark,hexaquark and nonaquark.Experimentally,a new hadron state,d~*(2380),has recently been found in the double?reaction of proton-neutron collisions.The mass of d*(2380)is just below the threshold of double?(1232)baryons and is quite difficult to be identified as the convenient baryon states.In this thesis,a constituent quark model is employed to investigate the mass spectra of the non-strange light hexaquarks with the same quantum number as d*(2380)with the purpose to further examine whether d*(2380)can be assigned to a non-strange light hexaquark state.The constituent quark model has two basic assumptions:first,the quarks bound within the hadron have constituent mass and move nonrelativistically and follow the Schrodinger equation;second,the interaction between quarks is descripted by the effective potential.Various quark potential models lie in the difference of specific forms of potential,but most potential models are based on Cornell potential.In this thesis,a relativistically modified quark potential model is adopted.The interquark interaction is mainly described by one gluon exchange potential in short range regions,and by the mixing of scalar and vector confinement potentials in long range regions.The harmonic oscillator basis and the group theory methods are used to construct the coordinate,spin,flavor and color space wave functions,so that the total wave functions is required to satisfy the full antisymmetry.Hamiltonian matrix of the hexaquark system is calculated and mass spectra of the hexaquark system are obtained by diagonalizing the Hamiltonian matrix with the combination of the variational method.In this work,taking space(0s)~6,(0s)~5(1s)~1 and(0s)~4(0p)~2 configurations into account,we calculate the mass spectra of non-strange light hexaquark states with the isospin(I),angular momentum(J)and parity(P)quantum numbers I(J)~P=0(3)~+,and then determine which of the hexaquark states with quantum number I(J)~P 0(3)~+may be d*(2380)states.The calculated results show that among total 16 states,there exist four states and their energies are 2365,2388,2401,2407 MeV,close to the experimental value of 2380 MeV without the considered mixing of configurations.With the configuration mixing,the energy of only one mixing state is very close to the experimental value 2380 MeV,and the energy of this mixing state is 2382 MeV.By expanding the resulting wave function,the hidden color channels is found to account for 80%of the mixing state,and thus such a mixing state is dominated by the hidden color channels.The thesis is consists of the four parts:The first part is an introduction,which briefly describes the development of particle physics,the commonly used non-perturbative QCD methods and the present research status of the hexaquark states.In the second part,the quark potential model adopted in this thesis is introduced,and one-gluon-exchange potential and linear confinement potential are given.The confinement potential is considered to be a mixing of scalar and vector confinement potentials.The third part introduces the numerical calculation method.The Hamiltonian in Jacobi coordinates,the space wave functions,spin,flavor and color,and the full-antisymmetric total wave functions as well as the calculation method of Hamiltonian matrix are presented.The fourth part is to analyze the mass spectrum of the non-strange light hexaquark states with quantum number I(J)~P=0(3)~+.