Investigations On The Quark-quark Hyperfine Interaction By Fitting The Spectrum And Decays Of Low-lying Baryon Excitations

As we known,the basic theories of strong interaction is the Quantum Chromodynamics which based on quark and gluon's degrees of freedom and its normative field theory.This theory is very successful at high energy region,but in the non-perturbative low energy region,it is difficulty to deal with the lower energy hadronic problems by the first principle of QCD because of the complex of the non-perturbative theory,many problems still cannot be solved by the QCD theory.In this region,the lattice QCD may be used.Although lattice QCD make a lot of progresses in hadron physics recently,it is still far from satisfactory,especially for the hadron-hadron interaction and multiquark states.And the calculations depend on the performance of the computer and complicated computational codes.Consequently,we must construct some effective phenomenological models inspired by the QCD theory to deal with the physical problems.It is well-known that the phenomenal models,which have the properties of QCD,achieve great success to describe the nucleon-nucleon interaction,spectrum of hadrons,charmonium and bottomnium states.Among the various models,the most successful one seems to be the traditional constituent quark model in either the non-relativistic or relativistic forms.In this paper,a series of investigations on the quark-quark hyperfine interaction by fitting the spectrum and decays of low-lying baryon excitations are carried out using the non-relativistic constituent quark model.Employing the constituent quark models,we can explain many physical problems,such as the masses,spins and magnetic moments of the baryons in the spatial ground state.But there are also limitations in this model.Two well known problems are the mass order inverse of the baryon resonances N^?9??7?1440?8?,?43??7?1405?8?and N^?9??7?1535?8?,and many missing states predicted by the quark model.So we must go beyond the simple quark model to solve these problems.In this paper,we have investigated mixing of the lowest-lying qqq configurations withJ^P?28?1/2^-caused by the hyperfine interactions between quarks mediated by Goldstone Boson Exchange,One Gluon Exchange,and both Goldstone Boson and One Gluon exchange,respectively.The first orbitally excited nucleon,?43?,?50?and?states are considered.Contributions of both the contact term and tensor term are taken into account.Our numerical results show that the configuration mixing in the three employed hyperfine interaction models are very different,although the dominant components of all the obtained physical states are almost the same in these models.The differences between the one gluon exchange model and Goldstone boson exchange model involve not only the absolute values,but also the signs of the probability amplitudes for the dominant components in several physical baryon resonances.Beacause this is a possible way to examine the hyperfine interaction models by investigations of the electromagnetic and strong decays of the baryon resonances using the present results,which should be very sensitive to the coefficients of the configuration mixing.So we calculate the strong decay widths for theJ^P?28?1/2^-baryon resonances to the pseudoscalar meson and octet baryon,and then compare results with experiment to test different models.We find that introducing symmetry-breaking effects due to one-gluon exchange?OGE?or Goldstone-boson Exchange?GBE?mechanism allows us to account for some partial decay widths of the N*and?*resonances,but both can not produce for all partial decay widths.And for the?and?hyperon,due to the missing experimental values,we can not distinguish the results support which model.In addition,it is very desirable to consider possible contributions from higher Fock components to produce better numerical results.