π介子的非对称发射与核媒质态方程

本文采用VUU模型研究了1.8AGeV Ar+Pb碰撞中π介子子非对称发射携带的核物质态方程信息.指出在靶核旁观者吸收较弱的入射核快度区域,末态π介子的集体运动中保留着同重子集体关联类似的特性.其发射方位角分布的非对称性是对核物质态方程敏感的参量.由π介子方位角关联函数方法对Bevalac激光室1.8AGeV Ar+Pb碰撞实验数据的分析结果和对硬核媒质态方程模型模拟事件的计算相符合.     

π介子理论的提出—记日本物理学家汤川秀树

汤川秀树是日本著名的理论物理学家,1935年,汤川秀树在物理界普遍 不接受新粒子的情况下,大胆提出一种新的核力场理论,认为存在起强相互的π介子,介子理论的提出,推动了核物理研究的发展,文章简要记述了这一历史事件。在介子理论提出10年后,π介子才被英国物理学家鲍威尔在宇宙射线中发现,实了汤川透树的假设,由于汤川秀树对物理学发展所作出的贡献,汤川秀树获得1949年诺贝尔物理奖。     

核介质中π介子的衰变常数

研究了核介质中π介子衰变常数fπ 随核介质密度 ρ变化的规律 ,指出了随着核密度的增加fπ 逐渐减小。在正常核物质密度 ρ0 (=0 .17fm3 )时 ,fπ 减小百分之三十三左右。这对于研究核物质中介子动力学和相对论重离子碰撞中夸克胶子等离子体相变都是十分重要的。     

2π干涉学中的多π关联

多π事件中多π关联对2π干涉学的影响可以用相关π对取样中的多π关联因子和背景中剩余关联因子的比值来表示.在数据分析中这两种关联因子部分抵消,在π源半径较小,事件π多重数较大时,它们在小相对动量区域的差别变大,多π关联对2π干涉学结果的影响将变得重要.多π关联因子的分布C_n－2(q)能够敏感地反映事件中的多π关联效果.对Bevalac流光室2.1AGeV Ne+Pb和1.8AGeV Ar+Pb实验数据进行的多π关联因子分析表明,前者事件中的多π关联效果大于后者.     

π0介子寿命的实验研究

QCD(Quantum Chromo Dynamics)手征反常理论主导了π0介子到两个 γ 光子的衰变.基于手征反常理论和手征微扰论的修正,对π0介子寿命的理论预测精度高达1％.高精度实验测量π0介子的寿命可以严格检验低能区的QCD理论和手征微扰论.本工作重点介绍了三种测量π0介子寿命的实验方法:直接测量法、双光子反...     

菲尔德–费曼模型中的介子碎裂函数

从菲尔德–费曼的叠代模型出发,考虑到入射夸克的味结构,研究了π介子的碎裂函数Duπ+,Ddπ+,和Dsπ+,并将分析结果和实验数据进行了比较,对K介子的碎裂函数DsK+(z),DuK+(z),DsK+(z)和DdK+(z)作出的预言将被进一步的实验检验。     

维数正规化和NJL模型π介子性质

利用定义于Grassmann扩展空间的Dirac代数算符表象的维数正规化方案,研究Nambu-Jona-Lasinio(NJL)模型中的π介子模式的性质.说明维数正规化方法可以给出NJL模型中强子模式的解析形式和相应的符合实验的数值结果.     

核物质中π分子引起的粒子–空穴和△-空穴激发

以π介子为例给出了正确计算核物质中粒子-空穴激发的相对论方法,指出了它与通常计算方法的区别及通常计算方法中所作近似的不合理性.并与非相对论的粒子-空穴激发的色散关系进行了比较.我们还用这一方法计算并给出了△-空穴激发的表达式.     

热密π介子环境中的ρ介子谱函数

利用描述ρ-π耦合的有效模型, 研究了热密π介子环境中的ρ介子谱函数.数值计算的结果表明, 随着温度和π介子化学势的升高, 谱函数变宽, 且峰的位置向高不变质量区移动.     

Diffraction model analysis of pion-12C elastic scattering at 800 MeV/c: Optical potential by inversion

Elastic scattering of 800 MeV/c pions by¹²C has been studied in the diffraction model with a view to determine pion optical potential by the method of inversion. Finding an earlier diffraction model analysis to be deficient in some respects, we propose a Glauber model based parametrization for the elasticS-matrix and show that it provides an exceedingly good fit to the pion-carbon data. The proposed elasticS-matrix gives a closed expression for the pion-¹²C optical potential by the method of inversion in the high energy approximation.     

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.     

Intermediate Energy Pion-~(20)Ne Elastic Scattering in the α+~(16)O Model of (20)~Ne

We present an analysis of π-20Ne elastic scattering at intermediate energy basing on the α+16O model of the20Ne nucleus and in the framework of Glauber multiple scattering theory. Satisfactory agreement with the general features of the experimental data of pion elastic scattering on the neighboring 4N-type nuclei is obtained without any free parameters. Compared with the experimental angular distributions of pion elastic scattering on12C,16O,24Mg,and28Si nuclei, the difractive patterns and the positions of the dips and peaks in the angular distributions of π-20Ne elastic scattering are reasonably predicted by the calculations.     

Effective-field theory and the nuclear many-body problem

We review many-body calculations of the equation of state of dilute neutron matter in the context of effective-field theories of the nucleon-nucleon interaction.     

相对论核多体研究进展

简要评述了相对论核多体理论最近的发展及其在核物质和有限核的微观描述方面的应用 ,所涉及的理论框架主要是相对论 Brueckner- Hartree- Fock理论和相对论平均场理论 .例举了某些最新的应用领域 ,同时也讨论了若干待解决的问题和可能开展的工作. Relativistic many body methods, which include the relativistic Brueckner Hartree Fock (RBHF) theory and the relativistic mean field (RMF) approach, were introduced, while their progress and application for nuclear matter and finite nuclei were presented. The open questions in this field and the trend in future were also discussed.     

密度相关袋常数的夸克介子耦合模型关于核物质和有限核的研究

由满足手征对称的Nambu-Jona-Lasinio(NJL)模型出发, 计算得到袋常数的密度相关性, 并将其与夸克介子耦合(QMC)模型相结合, 研究核物质和有限核的性质.结果表明, 该模型能够成功地描述核物质的性质, 但得到的有限核结合能过大, 其中重整势起了非常关键的作用.     

核物理发展现状分析和建议

对国内外核物理发展现状、前沿进行了简要分析和概括,对我国核物理发展优先资助领域提出了自己的一些看法和建议。A brief review is given on the frontiers of nuclear physics research. Some personal opinions and suggestions to the NSFC on the fields to have priority for support are presented.     

Strongly enhanced quadrupole deformation in a class of N≈Z nuclei driven by large-scale clustering?

The formation of large size clusters,and/or their relative motion as a possible excitation mode,are sugge sted to be closely related to the origin of deformation in specific cases,namely the case of two doubly-magic clusters or two clusters with nearby characterization.New lifetime data in N=Z ~(76)Sr and ~(80)Zr leading to large B(E2) values are reproduced consistently and well within this approach,along with data for a few neighboring N≈Z nuclei.These results are compared to previous studies of ~(32)S and ~(20)Ne and all of them support the ideas of the large-scale cluster approach.