夸克平均场模型研究有限核及超核

采用组分夸克模型描述重子,首先由自由核子及超子的性质定出模型参数,进一步考虑核介质中重子性质的变化,核介质中的介子平均场直接与重子内部的组分夸克相互作用.夸克平均场模型已被用于研究有限核及超核的性质,能够给出令人满意的有限核及超核的性质,该模型也预言了核介质中核子体积的膨胀及核子有效质量的降低. The quark mean field model, which describes the baryon by using the constituent quark model, is applied to study the properties of finite nuclei and hypernuclei. The meson mean fields couple directly with the quarks and change the properties of baryons in nuclear medium. The quark mean field model provides satisfactory results on the properties of spherical nuclei and hypernuclei. It also predicts an increasing size of the nucleon as well as a reduction of the effective mass in the nuclear environment.     

夸克的横向性分布与核子张量荷

夸克的横向性分布的一次矩定义了核子张量荷. 核子张量荷也可用张量流算符在核子态的矩阵元定义,由此用量子色动力学求和规则、有效理论和模型计算了核子张量荷. 对研究核子性质及强子物理的自洽非微扰途径问题也作了简要讨论. The first moment of quark transversity distribution defines the tensor charge of nucleon. The tensor charge of nucleon can also be defined as the forward matrix element of the tensor current in the nucleon state，which is used to study the nucleon’s tensor charge in terms of quantum color dynamics(QCD) sum rule approach， the effective theory and model. A consistent nonperturbative approach to study nucleon property and hadronic physics is also discussed.     

强和弱Y-Y相互作用下的奇异强子物质

把修正的夸克-介子耦合模型推广到包含奇异性的情形， 并用来研究奇异强子物质的状态方程. 从最新的6ΛΛHe双超核的实验导出的弱Λ Λ相互作用和过去采用的强Λ Λ相互作用同时被用于计算. 比较发现， 具有强Λ-Λ相互作用的系统束缚得比正常核物质要紧， 而具有弱Λ Λ相互作用的系统则比正常核物质束缚得要松得多. 无论强还是弱相互作用情况， 为了合适地描述修正的夸克 介子耦合模型中超子-超子（Y Y）相互作用， 必须引进σ*和介子. A modified quark meson coupling (MQMC) model is extended to include Λ hyperons and Ξ hyperons. The extended model is then used to study the equation of state (EOS) for strange hadronic matter. A weak Λ Λ interaction deduced from recent observation of 6ΛΛHe double hypernucleus is adopted in the calculation. The resultant EOS is compared with that deduced from a strong Λ Λ interaction. It is found that while the system with the strong ΛΛ interaction is more deeply bound than ordinary nuclear matter due to the opening of new degrees of freedom， the system with the weak Λ Λ interaction is rather loosely bound compared to the later. It is necessary to introduce the strange mesons σ*and in the MQMC model to describe properly the interaction between the hyperons in either strong or weak ΛΛ interaction case.     

手征胶子修正夸克平均场模型

这项工作利用考虑π介子与胶子效应的夸克平均场模型研究原子核结构的基本性质。在夸克平均场中,核子由三个束缚在谐振子势场中的组分夸克构成。描述强相互作用的量子色动力学必须满足手征对称性,此外夸克之间也需要通过交换胶子相互作用。因此,在夸克平均场模型中,对利用夸克势获得的核子质量考虑π介子修正与胶子修正。通过少数稳定有限核的结合能与半径实验值确定模型中的未知参数,获得了一组夸克平均场相互作用参数,QMF-NK。利用该组参数计算40Ca和208Pb的电荷密度分布,发现与实验值符合很好。随后获得了与经验值一致的对称核物质的饱和性质。包含π介子修正和胶子修正的夸克平均场模型能够更好地描述有限核和核物质的性质。The basic properties of nuclear structure are studied within the quark mean field (QMF) model by taking the effects of pions and gluons into account. In QMF, the nucleon is made up of three constituent quarks confined by a harmonic oscillator potential. The quantum chromodynamics describing the strong interaction must satisfy the chiral symmetry and quarks interact with each other through exchange of gluons. Therefore pion correction and gluon correction are included in the nucleon mass obtained by using quark confinement potential in quark mean field model. We determine the unknown parameters in the model by fitting the experimental data of the binding energies and radii of several stable finite nuclei and obtain a set of parameters of quark mean field interaction, named QMF-NK. The charge density distributions of 40Ca and 208Pb are calculated, which are in good agreement with the experimental data. Later the saturation properties of symmetric nuclear matter which are consistent with the empirical data are obtained. With the pion and gluon corrections, the QMF model could treat finite nuclei and nuclear matter better.     

核子自旋结构

简要介绍了夸克的发现、核子的夸克模型 ,详细讨论了夸克模型中核子内夸克自旋结构和极化轻子-核子深度非弹散射测量出的夸克自旋结构中的矛盾 .指出这个矛盾是由于对夸克自旋理解的混淆.最后还讨论了规范不变性和正则量子化两大物理学原则在夸克、电子轨道角动量上出现的矛盾. A simple introduction of the discovery of quark and the constituent quark model of nucleon have been given. The contradiction between the quark spin structure of nucleon of the constituent quark model and the measured one in the polarized deep inelastic lepton nucleon scattering has been explained in detail. It is elucidated that the so called “proton spin crisis” is due to quark spin confusion. The incompatibility between the requirement of gauge invariance and ...     

基于手征微扰理论构建相对论重子-重子相互作用(英文)

介绍了两个近期基于协变手征微扰理论构建领头阶核子-核子和超子-核子相互作用的工作。理论中未知的低能常数通过拟合核子-核子和超子-核子散射实验数据确定。分析发现,在对散射数据的描述上,领头阶相对论手征力可以媲美次领头阶非相对论手征核力。研究表明,构建相对论手征重子-重子相互作用技术上是可行的。得到的相互作用不仅可以为相对论核结构及反应研究提供重要的理论输入,而且可以进一步加深对低能强相互作用的认识。In this paper, we report on two recent studies of relativistic nucleon-nucleon and hyperonnucleon interactions in covariant chiral perturbation theory, where they are constructed up to leading order. The relevant unknown low energy constants are fixed by fitting to the nucleon-nucleon and hyperon-nucleon scattering data. It is shown that these interactions can describe the scattering data with a quality similar to their next-to-leading order non-relativistic counterparts. These studies show that it is technically feasible to construct relativist baryon-baryon interactions, and in addition, after further refinements, these interactions may provide important inputs to ab initio relativistic nuclear structure and reaction studies and help improve our understanding of low energy strong interactions.     

核物理中的π介子

在强子层次上,原子核或强子物质的基本组元是核子和介子.弄清这些强子的结构,并由基本原理出发研究它们的性质,是当代核物理的重要课题.在各种介子中,π介子是最轻且最重要的介子.关于自由空间中π介子的结构与性质、核介质内π介子的性质、π 核子相互作用与π 核相互作用等问题,始终受到相当多的关注.π介子在核物理中的作用直接联系着手征对称性,汤川秀树关于π介子的最初概念已经大大发展了.有清楚的实验证据表明,核内存在π介子的集体模式,这种集体模式与以前观测到的所有核集体运动模式截然不同.拟对π 核物理的研究现状及值得进一步研究的主要问题予以简要评述. At the hadronic level, nucleons and mesons are constituents of nuclei and hadronic matter. Understanding the structures of hadrons, finding the physics of how the properties of these particles arise from the first principle, are major interests in modern nuclear physics. Among mesons, the lightest and most important one is certainly the pion, thus it is no accident that its structure, properties (both in free space and in nuclear matter) and interactions with nucleons and nuclei have gotten considerable ...     

核子(强子)结构和性质的QCD研究

核子 (强子 )是夸克、胶子的束缚态 ,由量子色动力学 QCD描述。由于 QCD的基本特性(高能标度下的渐近自由、低能标度下色禁闭及动力学手征对称性破缺 ) ,对核子 (强子 )结构和性质的 QCD图象是标度相关的 .在高能标度下描述强子的是与探测强子结构的硬过程相联系的QCD部分子模型 .强子的夸克、胶子结构信息通过 QCD部分子求和规则得到 .QCD微扰论是适用的理论 .在低能标度时 ,必须发展 QCD非微扰途径来描述核子 (强子 )物理 .这里简要地讨论各种非微扰途径 (格点 QCD、Dyson- Schwinger方程、有效场论、QCD求和规则 )的某些结果和进展 ,并指出 QCD真空结构在描述低能标度下强子物理中担任重要角色 . The nucleon (hadron) is the bound state of guarks and gluons, which is described by the quantum chromodynamics (QCD). Due to the basic properties of QCD (the asymptotic freedom at the high energy scale, the color confinement and the dynamical chiral symmetry breaking at the low energy scale), the QCD picture for the nucleon’s (hadron’s) structure and property is scale dependent. At high energy scale, the QCD parton model, which is relative to the hard process for testing the...     

核子质量、 半径及夸克凝聚的核物质密度依赖性

简要介绍核物质中核子的质量、 半径及夸克凝聚的密度依赖关系基于QCD模型和QCD有效场论研究的现状, 并具体介绍整体色对称模型（GCM）的研究结果. GCM研究表明, 在小于临界密度的情况下, 核物质中核子的质量随核物质密度的增大而减小, 核子的半径和夸克凝聚随核物质密度的增大而增大. 当达到临界密度时, 核子质量减小为零, 核子半径变为无限大, 夸克凝聚突变为零, 进而提出一个核物质中手征对称性恢复的新机制. The status of the investigations on the nucleon mass, nucleon radius and quark condensate in the framework of QCD inspired models and QCD effective field theories is briefly reviewed. The results in the global color symmetry model (GCM) are described a little detailedly. The calculated results indicate that, before the maximal density is reached, the mass of a nucleon in nuclear matter decreases, the radius of a nucleon and the quark condensate increase very slowly, with the increase of the nuclear matter density. As the maximal nuclear matter density is reached, the mass of the nucleon vanishes gradually. The radius becomes infinite and the quark condensate vanishes suddenly. A new mechanism for the chiral symmetry restoration in nuclear matter is proposed.     

矢量介子的辐射衰变

介子的辐射衰变是低能强子物理研究的重要方向, 通过它能够揭示介子的结构和性质。从有效场论的观点来看,介子衰变主要包含光子和强子之间的相互作用。使用SU(3)对称性和VMD模型分别对矢量介子的辐射衰变进行了研究。 通过对实验数据进行拟和,给出了在两种情形下V→Pγ的衰变宽度的理论值,并得到赝标量混合角θP 为－6°。 Radiative decay of mesons is an important aspect in low energy hadronic physics,through which structures and properties of mesons can be revealed. In view of effective field theories, the radiative decay of mesons involves mainly interactions between photons and hadrons. In this paper,we investigate the decay of vector mesons by using SU(3) symmetry and the vector meson dominance model respectively. By fitting with experiments, we give the theoretic widths for V→Pγ in both cases and the mixing angle of pseudoscalars θP is －6°.     

Is There Really a Spin Crisis?

The matrix element of quark axial vector current is shown to be different from the nonrelativistic quark spin sum for a nucleon at rest. The nucleon spin content discovered in polarized deep inelastic scattering is shown to be accommodated in a constituent quark model with 15% sea quark component mixing. The relativistic correction and sea quark pair excitation inherently related to quark axial vector current reduce the nucleon axial charge and this reduction is compensated by the relativistic quark orbital angular momentum exactly and in turn keeps the nucleon spin 1/2 untouched. Nucleon tensor charge has similar but smaller relativistic and sea quark pair excitation reduction.     

核子碰撞截面的介质修正对多重碎裂的影响

利用同位旋相关的量子分子动力学模型研究了中能重离子碰撞过程中,同位旋相关的核子碰撞截面的介质修正对于多重碎裂的影响.结果表明:在包括动量相关作用在内的软势的情况下,介质修正明显地提高了自由核子的发射和中等质量碎片的多重性对于核子碰撞截面的同位旋依赖的敏感性.但对于原子核阻止敏感地依赖于核子碰撞截面的同位旋效应而不敏感地依赖于对称势的形式这一性质的影响并不明显,因此,原子核阻止对于核子碰撞截面的同位旋依赖的敏感性主要决定于自由核子碰撞截面的同位旋相关性.     

Form factor measurements with (P-)ANDA at FAIR

The high intensity and high energy antiproton beams which will be produced at FAIR open the possibility to determine time-like electromagnetic form factors in a wide kinematical range,through the annihilation reaction: p+(p-)→e++e-.The status of the proposed experiment as well as the expected results are presented on the basis of realistic simulations.The impact of these measurements on the understanding of the nucleon structure,of the asymptotic properties of form factors and of the reaction mechanism are discussed using model independent statements based on symmetry properties of the strong and electromagnetic interactions in connection with space-like data.     

Single π~0 electro-production in the resonance region with CLAS

We report the analysis status of single π~0 electroproduction in the resonance region to study the electromagnetic excitation of the nucleon resonances. The study is aimed at understanding of the internal structure and dynamics of the nucleon. The experiment was performed using an unpolarized cryogenic hydrogen target and 2.0 and 5.8 GeV polarized electron beam during the e1e and e1-6 run periods with CLAS at Jefferson Lab. The new measurements will produce a data base with high statistics and large kinematic coverage for the hadronic invariant mass (W) up to 2.0 GeV in the momentum transfer (Q~2) range of 0.3-6.0 GeV~2. Preliminary results will be presented and compared with the various model calculations.     

Mass differences and neutron pairing in Ca,Sn and Pb isotopes

Various estimates of the even-odd effect of the mass shell of atomic nuclei are considered.Based on the experimental mass values of the Ca,Sn,and Pb isotopes,the dependence of the energy gap on the neutron number is traced and the relationship of this characteristic to the properties of external neutron subshells is shown.In nuclei with closed proton shells,effects directly related to neutron pairing and effects of nucleon shells are discussed.     

Effect of confined one-gluon-exchange potential and instanton-induced interaction on nucleon–nucleon interaction

The effect of confined one-gluon-exchange potential and instanton-induced interaction potential in the singlet(~1S_0) and triplet(~3S_1) channels for nucleon–nucleon interaction has been investigated in the framework of the relativistic harmonic model using the resonating group method in the adiabatic limit with the Born–Oppenheimer approximation. The contributions of the different components of the interaction potentials have been analyzed.     

Nucleon Spin Structure Functions in the Resonance Region and the Duality

We discuss the nucleon spin structure function gl and the difference between the proton and neutrontargets gp1 - gn1 , based on quark model calculation. Quark-hadron duality for the nucleon spin structure function is alsoanalyzed. Effects of the △(1232) and Roper P11(1440) resonances on the spin structure function and on the differencegn1 - gn1 are mentioned. The results of different models for the Roper resonance are also addressed.     

Near-threshold η production in pp collisions

We study near-threshold η meson production in pp collisions within an effective Lagrangian approach combined with the isobar model, by allowing for the various intermediate nucleon resonances due to the π, η, and ρ-meson exchanges. It is shown that the ρ-meson exchange is the dominant excitation mechanism for these resonances,and the contribution from the N*(1720) is dominant. The total cross section data can be reasonably reproduced,and the anisotropic angular distributions of the emitted η meson are consistent with experimental measurements.Besides, the invariant mass spectra of pp and pη explain the data well at excess energy of 15 Me V, and are basically consistent with the data at excess energy of 40 Me V. However, our model calculations cannot reasonably account for the two-peak structure in the pη distribution at excess energies of 57 and 72 Me V, which suggests that a more complicated mechanism is needed at higher energy region.