Meson Cloud Effect on △(1232) Resonance Transition Properties with a Relativistic Quark Model Approach

Based on a relativistic quark model approach, the transition properties of the first nucleon resonance △(1232), and the coupling constants gπNN, g△πN are investigated. Tvo different vays to remove the center of mass motion are considered. The results of the relativistic approaches with and without center ofmass correction are compared with those of nonrelativistic constituent quark model. Moreover, pion meson cloud effect on these calculated observables is explicitly addressed. Better results are obtained by taking the pion meson cloud into account.

Nucleon Form Factors and N-△ Transitions in a Hypercentral Constituent Quark Model with Meson Cloud

We study the nucleon form factors and the nucleon-△（1232） transitions in a framework of hypercentral constituent quark model. The pion meson cloud effect is taken into account explicitly. Our results show that the pion cloud contributes substantially to the nucleon form factors as well as to the helicity amplitudes of △（1232）, and it gives an improved agreement compared to the experimental.

Λ resonances studied in K^-p→Σ~0π~0 in a chiral quark model

A chiral quark-model approach is extended to the study of the KN scattering at low energies. The process of K-p →∑0π0 at PK 〈 800 MeV/c （i.e. the center mass energy W 〈 1.7 GeV） is investigated. The A（1405）S01 dominates the reactions over the energy region considered here. Around PK -- 400 MeV/c, the A（1520）D03 is responsible for a strong resonant peak in the cross section. Our analysis suggests that there exist configuration mixings within the A（1405）S01 and A（1670）S01 as admixtures of the [70,2 1,1/2] and [70,2 8,1/2] configurations. The A（1405）SOl is dominated by [70,2 1, 1/2], and A（1670）Sol by [70,2 8,1/2]. The non-resonant background contributions, i.e. u-channel and t-channel, also play important roles in the explanation of the angular distributions due to amplitude interferences.

K^-p scattering and hyperon excitations in a chiral quark model

A chiral quark-model approach is employed to study theˉ KN scattering at low energies.The processes of Kˉp → Σ 0 π 0,Λπ 0 andˉ K 0 n at P K 800 MeV/c （i.e.the center mass energy W 1.7 GeV） are investigated.The analysis shows that the Λ（1405）S 01 dominates the processes Kˉp → Σ 0 π 0,ˉ K 0 n in the energy region considered here.Around P K 400 MeV/c,the Λ（1520）D 03 is responsible for a strong resonant peak in the cross section of Kˉp → Σ 0 π 0 andˉ K 0 n.To reproduce the data,an unexpectedly large coupling for Λ（1520）D 03 to KN is needed.In contrast,the coupling for Λ（1670）S 01 to KN appears to be weak,which could be due to configuration mixings between Λ（1405）S 01 and Λ（1670）S 01 .By analyzing Kˉ p → Λπ 0,evidences for two low mass S-wave states,Σ（1480）S 11 and Σ（1560）S 11,seem to be available.With these two states,the reaction Kˉp →ˉ K 0 n can also be described well.However,it is difficult to understand the low masses of Σ（1480）S 11 and Σ（1560）S 11 .The s-channel amplitudes for Kˉp → Λπ 0 are also larger than the naive quark model expectations.The non-resonant background contributions,i.e.t-channel and/or u-channel,also play important roles in the explanation of the angular distributions due to amplitude interferences.

Analysis of X（1576） as a Tetraquark State with the QCD Sum Rules

We take the viewpoint that X（1576） is the tetraquark state which consists of a scalar diquark and an antiscalar-diquark in relative P-wave, and calculate its mass in the framework of the QCD sum rule approach. The numerical value of the mass mx= （1.66 =k 0.14） GeV is consistent with the experimental data. There might be some tetraquark components in the vector meson X（1576）.

Determining the strange and antistrange quark distributions of the nucleon

The difference between the strange and antistrange quark distributions,δs（x） = s（x） ˉs（x）,and the combination of light quark sea and strange quark sea,Δ（x） =ˉ d（x） ＋ uˉ（x） s（x） ˉs（x）,are originated from non-perturbative processes and can be calculated using non-perturbative models of the nucleon.We report calculations of δs（x） and Δ（x） using the meson cloud model.Combining our calculations of Δ（x） with relatively well known light antiquark distributions obtained from global analysis of available experimental data,we estimate the total strange sea distributions of the nucleon.

ΔπN耦合以及πNN耦合的计算

通过相对论夸克模型并结合介子云的贡献 ,计算了ΔπN耦合常数以及πNN耦合常数 .计算结果表明了介子云对Δ( 1 2 3 2 )共振态的性质的重要作用 .

介子云对质子和中子形状因子的影响

利用夸克模型，考虑π介子云对质子，特别是中子的形状因子的影响，计算了质子和中子的电磁形状因子．对中子的性质给予了较好的描述．

σ介子云和质子轻味海夸克分布

在现有的介子云模型的基础上 ,进一步考虑σ介子云效应对计算质子中的轻味海夸克分布所带来的影响 .我们发现计算结果能够更好的符合关于 d(x) / u(x)的实验数据 ,同时对模型中的ω介子云的参数给出一个修正 ,表明在物理核子中发现Fock态 |Nω〉的几率是一合理的小值 .

相对论夸克模型和N-Δ能量劈裂

基于相对论夸克模型 ,在夸克层次上研究了N Δ的质量和二者的能量劈裂 ,通过引入了赝标量π介子云效应 ,得到了π和核子之间的耦合常数gπNN,以及单胶子交换势和单π介子交换势分别对N Δ能量劈裂的贡献 ,计算结果较好地与实验值得到了吻合 .另外我们还比较了相对论与非相对论夸克模型在处理上的不同 .

D^0D^^0＊(D^0D^0＊) system in QCD-improved many body potential

For a system of current interest（composed of charm, anticharm and a pair of light quarks）, we show trends in phenomenological implications of QCD-based improvements to a simple quark model treatment. We employ a resonating group method to render this difficult four-body problem manageable. We use a quadratic confinement so as to be able to improve beyond the Born approximation. We report the position of the pole corresponding to the D^0D^0＊ molecule for the best fit of a model parameter to the relevant QCD simulations. We point out the interesting possibility that the pole can be shifted to 3872 Me V by introducing another parameter I0 that changes the strength of the interaction in this one component of X（3872）. The revised value of this second parameter can guide future trends in modeling of the full exotic meson X（3872）. We also report the changes with I_0 in the S-wave spin averaged cross sections for D^0D^0＊-→ωJ/ψ and D^0D^0＊-→ρJ/ψ. These cross sections are important regarding the study of QGP（quark gluon plasma）.