Hadron Spectrum Based On The Nonrelativistic Quark Model

In this thesis, we studied the dynamics and static properties of possible hadronicmolecular with one boson exchange model and the meson spectrum with coupled-channel effect based on the non-relativistic quark potential model.In chapter I, we give a brief introduction of the non-relativistic quark potentialmodel. In chapter II, the basic concept of quark pair creation model is introduced andan application is given to show the calculation details.In chapter III, we have represented the short range interaction by heavier mesonsη¹,σ,ρandωexchange. The effective potentials between two hadrons are obtained bysumming the interactions between light quarks or antiquarks via one boson exchange.We first apply the one boson exchange formalism to the deuteron, then generalize toD Dˉ*/DˉD*, B Bˉ*/BˉB*, DD*, BB*, PV systems with C = B = 1 and C = *B = 1.The possible molecular states are studied in this chapter. Our results indicate that the1++ B Bˉ*/BˉB* molecule should exist, whereas DD* bound state doesn't exist. Westudied the relationship between the D Dˉ*/DˉD* molecule and X(3872). To understandthe nature of X(3872), the mixing between this D Dˉ*/DˉD* molecule and the conven-tional charmonium state should be further considered. The model has a few parametersand is quite general, it can be widely used to dynamically study the possible molecularcandidates.In chapter IV, we investigate whether the resonances X(1835), X(2120) and X(2370)newly observed by the BES collaboration could be conventional qqˉmesons. If theyare indeed canonical pseudoscalar mesons, the natural assignments areη¹(1760) andX(1835) as the second radial excitation ofη¹ andη¹ respectively, and X(2120) andX(2370) as the third radial excitation ofη¹ andη¹ . To do so we calculate all kinemati-cally allowed two-body strong decays ofη¹(3¹S₀),η¹ (3¹S₀),η¹(4¹S₀) andη¹ (4¹S₀) stateswithin the framework of 3P0 model. If the BES results forη¹(1760) are taken to be true,the theoretical predictions could be consistent with the experimental data. However,if the mass and width ofη¹(1760) are chosen to be the world average listed in PDG orthe DM2 measurement, the result is negative. Since theη¹ (3¹S₀) qqˉmeson would mixwith ppˉdue to the"dressing"effect and final state interaction, we suggest X(1835)is the mixture ofη¹ (3¹S₀) and ppˉmolecule. Under the assignment of X(2120) andX(2370) asη¹(4¹S₀) andη¹ (4¹S₀) qqˉmesons, X(2370) is predicted to be rather broad, so it is unlikely that X(2120) and X(2370) can be understood as the third radial exci-tation ofη¹ andη¹ simultaneously. Since X(2370) is close to the 0*+ glueball 2.3～2.6GeV predicted by lattice QCD, we suggest it may be a mixture ofη¹ (4¹S₀) meson andglueball.In chapter V, we speculate coupled-channel effects in some bottomonium-likestates based on nonrelativistic quark model and 3P0 model. We find that the massshifts and the B Bˉcomponent of the physical bottomonium caused by the coupled-channel effects are large. Moreover, we evaluate the mass spectrum in conventionalconstituent quark model, where the coupled-channel effects are not taken into account.We find that the hadronic loop effects can be partially absorbed into the re-choice of themodel parameters. However, the underlying physics is different. In the scenario withcoupled-channel effects, there are sizable B Bˉcomponents in the physical bottomo-nium states. As a result, the production and decay of bottomonium would be differentfrom those predicted in quenched quark model. But both potential models with andwithout coupled-channel effects don't predict state with mass around 10890 MeV, weconclude Yb(10890) should be an exotic state beyond quark model. Moreover, the massspectrum predicted in our work can be used as a reference to determined whether thenew bottomonium-like state observed in future can be accommodated as a canonicalbottomonium and its assignment if it is.In chapter VI, the results and conclusions of this thesis are summarized.