质子自旋疑难及研究现状

ＮＭＣ实验结果是实验向理论提出的一个很有意义的课题。本文总结了质子自旋的唯象研究成果，提出对质子波函函数重新作动力学计算可能有助于人们加深对质子自旋的理解。     

夸克激发与质子自旋

提出一种新的重子波函数,它由SU(6)对称的三夸克组态和伴随的海夸克激发与价夸克激发组态构成.用此波函数对GA/GV,μP/μn及夸克自旋对质子自旋贡献的计算结果与实验数据符合甚好.     

质子自旋性质的研究

考虑了正、反海夸克对和胶子混杂态对质子波函数的影响，质子的一些自旋相关性质：轴矢流耦合常数ＧＡ／ＧＶ，结构函数ｇ１ｎ和ｇ１ｐ的计算得到了改进．     

质子的自旋危机问题

建立了质子自旋依赖的结构函数的第一矩与GDH求和规则之间的关系.根据这个求和规则和重子结构的[SU_sf(6)⊙O(3)]⊙SU_c(3)夸克模型,讨论了质子的自旋问题,并把理论的结果与EMC和SLAC的实验作了比较,结果相一致.发现在低动量转移区,P₃₃(1232)的光激发的贡献是最重要的,而且是负的.在高动量转移区,P₃₃的贡献是正的,而且随Q²的增加很快减小,可以略去,从负值到正值的转折点是在Q²=0.32GeV²附近.     

核子自旋的来源

在美国Thomas Jefferson国家加速器装置(Jlab)上工作的一个研究组确定了质子中夸克自旋的取向．简单地讲，自旋可以看作是指向一定方向并具有一定强度的微小的磁棒，有关夸克自旋的信息可以提供在核子中夸克如何分布的细节．     

CEBAF和质子G°实验研究

本文简单介绍了美国ＣＥＢＡＦ（连续电子束流加速器）的近况和研究方向,以及Ｃ厅将展开的研究核子内Ｓ夸克成分的极化电子与质子散射宇称破坏不对称性测量的实验,即质子味单态电形状因子Ｇ°实验． The current status and scientific goal of CEBAF (The continuous Electron Beam Accelerator Facility ) are briefly presented. The project of the measurement of the flavor Singlet form factor G°of proton at C hall is outlined. A precise measurement of Parity violating asymmetry in the scattering of polarized electron from a proton target enables one to explore the Strange quark content in the proton.     

在CP MAS NMR中测量质子自旋扩散速率的方法

自旋扩散在固体核磁共振的许多现象中都起着非常重要的作用。现有几种理论方案以估算扩散系数。然而在实践中这种估算既不实际也不可靠。本文提出了确定自旋扩散速率的新方案,它利用的是CP MAS NMR中的稀核退极化规律。带质子的稀核磁化矢量在退极化中表现出两个阶段,慢衰减的第二阶段是单一指数过程,它提供了自旋扩散速率的直接度量。自旋扩散实质上是极化转移的一种宏观表现形式,这种转移通过一系列成对自旋的flip-flop进行,可以用一维随机走步模型描述。从退磁过程半对数曲线的斜率可以求得平均flip-flop时间。自旋扩散系数可以由此估算。在一些典型的刚性有机固体和结晶高分子聚合物中,求得平均flip-flop的时间是700微秒左右。它比偶极相关时间大一个数量级。这意味着,自旋扩散时间常数与自旋—自旋弛豫时间常数是很不相同的,虽然这两个相应过程虽密切相关的。由质子线宽估计自旋扩散系数是不可靠的。     

极化海夸克对激发对核子的自旋相关性质的影响

分析各种极化的海夸克对对核子的自旋相关性质的作用. 并试图改进传统模型对质子自旋性质的计算.     

Quark, Gluon, Odderon Contributions to Total Cross Section of Proton-Proton Elastic Scattering at High Energies

Based on the quark-gluon structure of nucleon and the existence of Odderon in nucleon via gluon selfinteraction, the elastic scattering of pp at high energies is studied. Our theoretical predictions reproduce experimental data perfectly. The contributions from individual terms of quark-quark, gluon-gluon interactions, quark-gluon interference and the Odderon terms to total cross section are analyzed. In addition to the leading quark-quark contribution, the Odderon contribution is quite important. In particular, the Odderon plays an essential role in fitting to data. Therefore, We may claim that the high energy pp and pp elastic scattering may be good processes to search for the Odderon, the three Reggeized gluon bound states.     

重子产生中"自旋抑制"的原因及普适性

高能反应中,自旋3+/2重子的产生与1+/2重子相比,受到反常的极强抑制.本文证明这是夸克味道守恒的结果:多重产生中奇异夸克抑制.λ=/<1,决定了十重态重子只能以确定比例β与八重态重子一起产生,而且β=1+λ/3+2λ     

Proton Spin and Chiral Dynamics

 Recent successful chiral models for the spin fractions of the proton rely on parametrizations that are inconsistent with deep inelastic lepton scattering unless the quark masses are neglected and inconsistent with chiral quark models based on constituent quarks, because only chiral spinflip transitions are considered. Non-spinflip transitions are important for constituent quarks as they depend on the quark masses. Therefore, the models are valid at a scale of about 0.63 GeV to Λ_χ, where dynamical quark masses are expected to be close to current quark masses, rather than Λ_QCD. When constituent quark masses are properly included, chiral quark models generate spin fractions that disagree with the proton spin data. Received July 1, 1998; accepted for publication January 30, 1999     

中能强子－核物理的现状与问题

中能强子与核的散射研究发现,４００ＭｅＶ以上似乎普遍存在着截面理论值偏低的现象,例如,质子－核（ＰＡ）散射、π介子－核（πＡ）散射、ｋ分子－核（ｋＡ）散射的微分戳面传统理论值比实验结果约低２０％．引入相对论动力学可使ＰＡ散射理论结果大为改善。然而,在核子层次上的各种修正对介子－核散射的理论结果改善甚小．人们正在从更深入的非核子自由度寻找原因. Traditional theoretical investigations of the hadron-scattering cross sections ina wide range of nuclei in the intermediate-energy region (above 400MeV) have revealed obvious discrepancies with the existing experimental data. It is about 20% lower than the datafor hadronic probes such as proton,pion and kaon. For proton-nucleus sacattering, an agreement with experiment may significantly be improved by introduction of relativistic dynamices. For meson probes, however...     

The Spin Crisis of the Proton

The relationship between the Gerasimov-Drell-Hearn(GDH)sum rule and the first monent,ΓP-the proton spin dependent structure function integral,is established.According to the sum rule and quark structure model of baryon,[SU_sf(6)⊙O(3)]⊙SU_c(3),the spin problem of the proton is discussed The present theoretical results are also compared with the data measured by EMC and SLAC groups.Our prediction is in good agreement with the data.We find that the P₃₃(1232)photo-cxcitation dominates the spin structure function integrals and contributes negatively at low momentum transfer.At higher momentum transfer,the contribution of the P₃₃ is positive,and it decreases rapidly as Q² increasing and finally becomes negligible The integral changes its sign from negative into positive at about Q²=0.3GeV².     

Proton Spin Structure Functions and Quark-Hadron Duality

Quark-hadron duality of three proton spin structure functions g1, g2 and gT are discussed simultaneously. It is found that the onsets of the quark-hadron dualities of g1^p, g2^p and gT^p. are similar and they are expected to be at about Q2～2 GeV2. In addition, our results show that the elastic peak remarkably breaks local quark-hadron duality.     

Contribution of Sea Quarks and Gluons to the Proton Spin

Contributions of sea quark and gluon spins to the proton spin in Drell-Jahn processes and direct production of photons in proton-proton and proton-antiproton collisions are studied in the present work. Analytical expressions for two-spin asymmetries and are derived. In both processes, these asymmetries are studied and analyzed as functions of the kinematic variables , x _T, and x _F. Measurements of two-spin asymmetries and make it possible to determine the individual contributions of sea quark and gluon spins to the proton spin.     

The Problem of Gauge Invariance in the Current Study of Nucleon Spin

Instead of the popular gauge-dependent decomposition of the total angular momentum operator in QCD, we derived a gauge-invarian t one with better classical correspondence. We also explored the possibility that the requirement of gauge invariance and classical correspondence wiU partly contradict with the commutation relationship of momentum and angular momentum.     

Spin physics at JINR: Present and future

A short review of spin physics program at JINR is presented. The proposals on spin program at the NICA collider are discussed. The main purpose of this program is to study the nucleon spin structure and other phenomena with polarized proton and deuteron beams.