基于相对论Hartree-Fock理论的原子核壳结构性质研究

一直以来,原子核壳结构是原子核物理研究的重点关注内容。特别是随着近年来新一代放射性核束装置和探测技术的蓬勃发展,丰中子原子核中新的壳结构及其演化与形成机制等成为核物理关注的热点之一。在基于核力介子交换图像建立的相对论Hartree-Fock 理论框架下,本工作以Ca同位素、双幻核 208Pb、超重核以及极端丰中子核为例,综述丰中子原子核中新的壳结构形成机制,高角动量态赝自旋对称性恢复与介质中核力吸引-排斥平衡,赝自旋对称性恢复/破缺与原子核壳结构、新奇现象等研究工作,并着重关注了与原子核新壳结构形成、赝自旋对称性恢复以及新奇现象等密切相关的交换(Fock)项效应。     

核力与电荷无关吗

 在核物理教科书中,几乎都要讲到核力的电荷无关性,或者说同位旋不变性。所谓核力与电荷无关是指一对核子,不论是中子－中子,质子－质子或中子－质子,只要处于同样的空间状态和自旋状态,就具有相同的核力作用。核力的电荷无关性也可表述为两个核子之间的作用与两个核子的总同位旋投影Ｔ３无关。但是,核力的电荷无关只是近似成立,核力在同位旋空间的转动不变性,并不是绝对的,而是存在着破缺。这种破缺包括电荷无关性破缺（ＣＩＢ）和电荷对称性破缺（ＣＳＢ）,总共约有１％的量级。关于这种破缺的根源和对核物理各方面的影响已有不少研究。     

自旋与手征动力学的输运模拟研究

自旋相关的物理是多个研究领域的热门课题。核子和夸克都是自旋为1/2的费米子,在非对心重离子碰撞中受到自旋-轨道相互作用以及磁场的影响,会产生有趣的自旋动力学,特别是在垂直于反应平面方向上会出现自旋极化。在相对论重离子碰撞中,由于产生了极端的高温高密环境,夸克可以近似看作无质量粒子,此时自旋动力学过渡为手征动力学。在外界电磁场、涡旋场作用下以及在电荷与手征荷不对称的条件下,会产生一系列手征反常效应。本文介绍我们课题组基于输运模拟在自旋与手征动力学方面开展的一系列研究工作,包括中能重离子碰撞及相对论重离子碰撞中粒子的自旋极化、理想体系及相对论重离子碰撞中的手征磁波等。     

核物质中的三体核力效应和相对论效应

在BHF理论框架内,利用两体现实核力和微观三体核力研究了核物质状态方程,仔细计算和分析了核介质中不同的基本微观过程导致的三体核力对核物质状态方程的贡献,与相对论DBHF方法的计算进行了比较.结果表明,DBHF方法中包含的对核物质状态方程的主要相对论修正来自于核介质中伴随着自由核子–反核子对虚激发中间过程对核子相互作用中标量σ介子交换过程介质修正效应所导致的三体核力,而来自于其他的基本微观过程的三体核力对核物质状态方程的贡献并不能完全相互抵消,它们的总贡献甚至在饱和密度附近也是不能忽略的     

介绍一种“π凝聚”的理论模型

一、引言 π分子是一种基本粒子,属介子旅.根据据所带电荷为 、 、0,可分为π ,π-,πu三种π介子π介子的自旋转为零,宇称为负,同位旋为1,静止质量为139, 物理MeV,寿命为10-8see.它在核物理中占有十分突出的地位.自从1935年日本　川秀树提出了核力介子理论以来,现在一般都认为,核子-核了间的相互作用是通过π分子来传递的。在原子核内存在着瞬时出现的π介子,与自由π介子不同,它不满足的质能关系式,因此说它是“虚”的π介子. 最近几年,有不少理论物理工作者[1]在探讨这样一个问题:在原子核内是否有真实的自由π介子存在?他们考虑的基点…     

核物理与加速器未来一瞥

核物理过去把核看作单核子壳层模型的简单图象,现在已经转向把核看作有限饱和多体系统。GeV 电子加速器和重离子碰撞机是能够进行此类研究的两种未来加速器类型。     

核子–核子散射过程的研究和矢量介子交换势

在推广的手征SU(3)夸克模型下讨论了核子–核子散射过程和矢量介子交换势.给出了赝标π介子和矢量ρ和ω介子的GCM中心力的交换势和NN散射14个分波的相移.研究表明,矢量介子交换势可以替代单胶子交换势以解释核力的短程排斥.     

自旋极化核物质的状态方程

在Brueckner-Hartree-Fock理论框架内,研究了自旋极化核物质的状态方程及其自旋依赖性,计算了相关的物理量如朗道参数G₀和G′₀,并着重讨论了三体核力的影响.结果表明:在整个自旋极化度范围内,自旋极化核物质的每核子能量随中子和质子自旋极化度的变化相当精确地满足二次方规律,而且在Brueckner-Hartree-Fock理论框架内,自旋非极化核物质的能量总是比相应的自旋极化核物质的能量低,这表明核物质中不会发生由自旋非极化态向自旋极化态的自发相变.当密度较低时,三体核力对核物质状态方程的自旋依赖性的影响不明显;随着密度的增大,三体核力效应增强,而且三体核力使朗道参数G₀和G′₀增大,从而使核物质对于自旋涨落的稳定性增强     

串列加速器核物理国家实验室简介

中国原子能科学研究院的串列加速器核物理国家实验室成立于1987年.该加速器上配有双等源、电荷交换源、溅射源、强流溅射源和正在研制的极化源,已为核物理实验工作提供了20多种元素的离子束.该加速器上建有11条束流线,分布在三个实验厅中,主要的终端实验     

重离子碰撞中的矢量介子自旋排列

在非对心相对论重离子碰撞中,参与反应的系统具有巨大的轨道角动量,从而使产生的夸克胶子等离子体具有极强涡旋场,并通过自旋-轨道相互作用导致部分子的自旋极化,经过强子化导致重子的自旋极化以及矢量介子的自旋排列等可观测效应.矢量介子的自旋排列是指其自旋密度矩阵的00元素ρ00偏离1/3.在矢量介子衰变到两个赝标介子的过程中,衰变产物的极角分布只与ρ00有关,以此可以对自旋排列进行测量.理论研究表明,重离子碰撞过程中,重子的自旋极化反映了夸克自旋极化的时空平均效应,而矢量介子自旋排列则反映了夸克反夸克自旋极化的局域相空间关联.本文回顾了相对论重离子碰撞中矢量介子自旋排列的相关理论工作.重点以非相对论夸克融合模型为例,明确地计入夸克极化的相空间依赖性,展示了矢量介子自旋排列与夸克反夸克自旋极化特别是它们之间相空间关联的关系.本文还讨论了涡旋、电磁场、有效φ介子场以及它们的局域涨落对φ介子自旋排列的贡献,结果显示强作用场的时空关联效应是导致φ介子自旋排列的主要因素.矢量介子自旋排列为探索强相互作用物质和强相互作用场的性质提供了新途径.     

Recent HERMES Results on DVCS from Proton and Nuclear Targets

Spin structure is one of the fundamental subjects in the study of nucleon structure.Recently it is found that Generalized Parton Distributions(GPDs) are related to the total angular momentum carried by partons,which offers a possible solution to the spin puzzle in the first time.We get access to certain GPDs by looking at the azimuthal angle asymmetries attributed to the interference between Deeply Virtual Compton Scattering (DVCS) and Bethe-Heilter processes in HERMES experiment.By measuring the asymmetry with respect to transverse target polarization from proton target,a model-dependent constraint on J_u vs J_d is obtained.Another worldwide unique channel is nuclear DVCS.The preliminary results on asymmetries with respect to beam spin and beam charge are reported.     

利用SLEGS开展夸克和胶子层次上的核物理研究

通过对国际上中能核物理的发展,特别是前沿领域中的现状的回顾,阐述了利用在上海原子核所计划建造的第三代同步辐射加速器(SSRF)上建立新一代的激光 电子康普顿背散射γ射线源(SLEGS)从事夸克和胶子层次上的中能核物理研究的科学目标及研究内容. The proposed SLEGS (Shanghai Laser Electron backscattering Gamma Source) will be a circular and linear polarization, new generation, high quality γ ray source with Eγ=0.2-0.87 GeV. The major scientific focus of nuclear physics research at SLEGS will be investigations of the microscopic quark gluon aspects of nucleons , nucleon resonance states and nuclei to test and develop non perturbative QCD. Using polarized photon induced reactions on unpolarized and polarized nucleon target such as γN→γ N, ...     

Electron-ion collider in China

Lepton scattering is an established ideal tool for studying inner structure of small particles such as nucleons as well as nuclei. As a future high energy nuclear physics project, an Electron-ion collider in China (EicC) has been proposed. It will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy-ion Accelerator Facility (HIAF) which is currently under construction, together with a new electron ring. The proposed collider will provide highly polarized electrons (with a po- larization of 80%) and protons (with a polarization of 70%) with variable center of mass energies from 15 to 20 GeV and the luminosity of (2–3)×10³³ cm−2•s−1. Polarized deuterons and Helium-3, as well as unpolarized ion beams from Carbon to Uranium, will be also available at the EicC.The main foci of the EicC will be precision measurements of the structure of the nucleon in the sea quark region, including 3D tomography of nucleon; the partonic structure of nuclei and the parton interaction with the nuclear environment; the exotic states, especially those with heavy flavor quark contents. In addition, issues fundamental to understanding the origin of mass could be addressed by measurements of heavy quarkonia near-threshold production at the EicC. In order to achieve the above-mentioned physics goals, a hermetical detector system will be constructed with cutting-edge technologies.This document is the result of collective contributions and valuable inputs from experts across the globe. The EicC physics program complements the ongoing scientific programs at the Jefferson Laboratory and the future EIC project in the United States. The success of this project will also advance both nuclear and particle physics as well as accelerator and detector technology in China.     

Quasi-free (e,e'N) reactions on polarized targets

The quasi-free nucleon knockout by the electron is studied in the general case of both polarized beams and polarized targets. The coincidence cross section involves nine structure functions which give detailed information on the nuclear current operator. However, their measurement requires out-of-plane experiments. Results on ⁷Li and ³⁹K obtained within the nonrelativistic DWIA framework indicate that some structure functions, very sensitive to final state interactions, are probably too small to be separated. On the other side, cross sections, asymmetries and electron polarization ratios in coplanar kinematics have measurable size. They add complementary information to the unpolarized quasi-free nucleon knockout because of their sensitivity to spin degrees of freedom which are averaged out without target polarization. In the particular case of a nucleon ejected along the direction of the momentum transfer from a target with spin oriented in the same direction (superparallel kinematics) only three structure functions survive and can be simply separated.     

Twist-3 single-spin asymmetries in semi-inclusive deep-inelastic scattering

The single-spin asymmetries for a longitudinally polarized lepton beam or a longitudinally polarized nucleon target in semi-inclusive deep-inelastic scattering are twist-3 observables. We study these asymmetries in a simple diquark spectator model of the nucleon. Analogous to the case of transverse target polarization, non-vanishing asymmetries are generated by gluon exchange between the struck quark and the target system. It is pointed out that the coupling of the virtual photon to the diquark is needed in order to preserve electromagnetic gauge invariance at the twist-3 level. The calculation indicates that previous analyses of these observables are incomplete.     

Theory of the polarization of highly charged ions in storage rings: Production, preservation, observation and application to the search for a violation of the fundamental symmetries

Theoretical concepts for the production, preservation and control of polarized highly charged ion beams in storage rings are investigated. It is argued that hydrogen-like ions can be polarized efficiently by optical pumping of the Zeeman sublevels of ground state hyperfine levels and that the maximum achievable nuclear polarization exceeds 90%. In order to study the preservation of the polarization during the ion motion through the magnetic system of the ring, the concept of the instantaneous quantization axis is introduced. It is suggested that the employment of “Siberian snakes” may help to preserve the ion beam polarization in the ring. The control of the beam polarization can be achieved by different methods: by measuring the Stokes parameters for the emitted photons or by observing the angular dependence of the transition rates for polarized ions. The important motivation for the production of polarized ion beams is the possibility to observe parity nonconservation effects in the hyperfine-quenched transitions in helium-like highly charged ions, where these effects can reach an unprecedented high value for atomic physics. The possible observation of parity nonconservation effects connected with the nuclear anapole moment is also discussed. A method for the observation of the electric dipole moment of an electron in a storage ring with a polarized highly charged ion beam is proposed. This method allows, in principle, to improve the existing boundaries for the electric dipole moment of an electron. However, the requirements of the corresponding experiment are very stringent.     

Recent results from COMPASS spin program

COMPASS is a fixed target experiment at CERN’s Super-Proton-Synchrotron. Part of its physics program is dedicated to the spin structure of the nucleon, which it studies with a polarized muon beam and polarized targets. An overview of its recent results along this line is given. In particular, the first results of our 2011 longitudinally polarized proton run, a report on our progress towards the extraction of the gluon polarization, ΔG, at NLO and an update on our measurements of transverse spin and k _T -dependent processes, from our 2010 transversely polarized proton data, and of hadron multiplicities.     

Spin-polarized nuclei as probes of electromagnetic field distributions on solid surfaces

Recent experiments using thermal beams of nuclear-spin-polarized alkali atoms adsorbed on hot metal surfaces show that polarized nuclei are sensitive probes of surface electromagnetic field distributions. The high polarization of the probe beams, when coupled with the efficiency of atomic physics techniques used for monitoring the polarization of desorbed particles, makes possible a variety of interesting spinrelaxation experiments on single-crystal surfaces, including nuclear magnetic resonance. Extension of the current experimental method to semiconductor and insulator surfaces at arbitrary temperatures appears to be straightforward. The information from spin-polarized nuclear surface spectroscopy (SPNSS) will allow detailed tests of charge-density profiles now available in self-consistent surface structure calculations. Moreover, the variety of presently available polarized nuclear species suggests that the chemistry of many interesting adsorbate-surface systems could also be profitably investigated by this technique. The use of spin-polarized hydrogen nuclei in particular offers enticing prospects for fundamental studies in catalysis, surface structure and basic two-dimensional physics.     

Nucleon transport processes in fission and heavy ion reactions

The nucleon exchange process between two nuclei in close proximity and its application to an explanation of fragment mass and charge distributions in fission and in heavy ion deep inelastic collisions are reviewed. An analysis of the measured correlations between the energy loss from relative motion and the fragment mass and charge variances in the heavy ion deep inelastic collisions is presented. The recent data on fragment mass and charge variances as a function of the fragment kinetic energy in thermal neutron induced fission of²³⁵U, lends added support to the hypothesis that the nucleon transport process plays a similar role both in fission and in heavy ion deep inelastic collisions.