e-p深度非弹性散射中粲夸克态的效应

本文利用质子存在粲夸克态│uudcc〉, 将它的效应和原有的Buras等人计算的结果迭加起来, 能够使e-p深度非弹性散射中所预言的纵横虚光子吸收截面比R=σ_L/σ_T与实验值较好地符合.     

大横动量的部分子在深度非弹性散射中的行为

本文把核子态用FOCK空间各个组态分量来表示, 并且在结构函数中引入了部分子的横动量作为一个自由度, 计算了价夸克态分量和非价夸克态中的粲夸克分量对虚光子纵横截面比的贡献, 结果与实验数据符合较好. 同时找到了Callan-Gross关系与实验数据偏离的因素.     

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.     

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.     

FF模型在pp软碰中的应用

本文将夸克喷注的Field-Feynman模型推广应用到pp反应中, 并且提出一个关于双夸克碎裂的方案, 从而改进了A.Capella的双链模型. 这一图象既能给出各种粒子(介子, 重子, 光子, 夸克对等)的平均产额和能量的关系, 又能计算各种单粒子的内含谱及关联效应. 计算结果和实验数据符合很好.     

共振双光子吸收光谱的一种新方法

本文提出共振双光子吸收光谱的一种新的实验方法.实验装置与双光子荧光法测超短脉冲脉宽的装置是一样的.在测定了信号强度的反差比以后可以推知完全共振双光子吸收截面与两步单光子吸收截面之比值.理论计算表明,本方法的适用范围是相当大的.     

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.     

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 ...     

含时电离对分子动态双光子吸收截面的影响

通过采用时域有限差分法和预估矫正法数值求解麦克斯韦-布洛赫方程,研究了含时电离对分子材料4,4'-二甲氨基二苯乙烯的动态双光子吸收截面的影响.研究结果表明,对周期量级的飞秒脉冲,介质发生的主要是一步共振双光子吸收,入射光强较高时出现双光子吸收饱和现象,入射光强小于双光子吸收饱和光强时介质的双光子吸收截面随入射光强的增大线性减小.在不同的传播距离处,分子的双光子吸收截面有较大的差别,因此,在对不f川的实验条件下测得的双光子吸收截而数值进行比较时,需要考虑样晶厚度对实验结果的影响.在同一传播距离处,随光电离截面取值的增人介质的双光子吸收截面减小.利用匕秒脉冲测量分子的双光子吸收截面时,通过数值模拟,讨论了已有解析结果的适用条件.     

超高能重离子碰撞中大横动量光子产生和QCD退禁闭相变信号

本文讨论了夸克胶子等离子体发射大横动量光子的机制,并用来分析日美合作组的实验结果.结果表明,大横动量光子是退禁闭相变的一种实验信号.     

Spin Dependent Quark Forces and the Spin Content of the Nucleon

The spin crisis of the nucleon is that the quark spin contribution is only a small fraction of the nucleon spin. A relativistic Dirac equation approach is followed assuming three low mass current quarks in the nucleon described by a (1/2⁺)³ configuration. If the lower component contribution to the normalization of the quark wave function is about 0.18, then the axial charge of the nucleon can be reproduced. However including the same lower component to every quark wave function is not enough to resolve the spin crisis. The net u quark spin z component is predicted as 1.0 and the net d quark spin z component is predicted as –0.25, both in disagreement with experiment. These predictions can be brought into agreement with experiment if flavor independent but spin dependent forces are assumed between the quarks. The strength of the spin dependent force found by empirically fitting the nucleon spin data is shown to be comparable to the spin dependence that can explain the -nucleon mass difference. The spin content of the ⁺ is then predicted using the interactions that reproduce the spin content of the proton.     

Evidence for a single-spin azimuthal asymmetry in semi-inclusive pion electroproduction

Single-spin asymmetries for semi-inclusive pion production in deep-inelastic scattering have been measured for the first time. A significant target-spin asymmetry of the distribution in the azimuthal angle straight phi of the pion relative to the lepton scattering plane was formed for pi(+) electroproduction on a longitudinally polarized hydrogen target. The corresponding analyzing power in the sinstraight phi moment of the cross section is 0.022+/-0.005+/-0.003. This result can be interpreted as the effect of terms in the cross section involving chiral-odd spin distribution functions in combination with a chiral-odd fragmentation function that is sensitive to the transverse polarization of the fragmenting quark.     

Spin Correlations in Top Quark Pair Production Near Threshold at the e+e- Linear Collider

We investigate the spin correlations in top quark pair production near the threshold at the e e- linear collider. Comparing with the results above the threshold region, we find that near the threshold region the off-diagonal basis, the optimized decomposition of the top quark spins above the threshold region, does not exist, and the beamline basis is the optimal basis, in which there are the dominant spin components: the up-down (UD) component for e-Le scattering and the down-up (DU) component for e-Re scattering can make up more than 50% of the total cross section,respectively.     

Spin Correlations in Top Quark Pair Production Near Threshold at the e^＋e^- Linear Collider

We investigate the spin correlations in top quark pair production near the threshold at the e^ e^- linear collider. Comparing with the results above the threshold region, we find that near the threshold region the off-diagonal basis, the optimized decomposition of the top quark spins above the threshold region, does not exist, and the beamline basis is the optimal basis, in which there are the dominant spin components: the up-down (UD) component for e^-le^ scattering and the down-up (DU) component for eR^-e^ scattering can make up more than 50% of the total cross section,respectively.     

Λ超子碎裂函数的夸克味分离

利用有非极化和极化的A和A超子产生的中微子和反中微子的深度非弹性散射,可以清晰地测量各种味的夸克变为A超子的各种非极化和极化的碎裂函数,也就是得到了碎裂函数的夸克味分离.这种方法不但适用于轻味夸克。反夸克,也适用于奇异夸克s和s.和产生A和A的极化电子的深度非弹性散射结合起来,人们就能够系统地测量或核实各种味和各种自旋的夸克的相关碎裂函数.这样的测量给有关强子的自旋结构和核子海的夸克一反夸克不对称性的各种预言提供判决性的实验.     

Recent results from the HERMES experiment

Results are presented from the Hermes experiment which uses semi-inclusive deep inelastic lepton scattering to study the flavor structure of the nucleon. Data have been accumulated for pion and kaon double spin asymmetries, single-spin azimuthal asymmetries for meson electroproduction, deep virtual Compton scattering (DVCS), and meson multiplicities. These results provide information on the properties of the strange sea in the proton, constraints on transverse momentum dependent quark parton distributions, and demonstrate the promise of DVCS for isolating the total angular momentum carried by the quarks in the proton.     

Phenomenology of the proton spin

We analyze the various inputs that go into computing the recently measured first moment of the proton spin structure functiong ₁ ^p (x). The basic inputs are the various valence and sea quark polarisations and the gluonic contribution coming through axial anomaly. We show that the quark model predictions for valence quark polarisations, suitably modified to accommodate Bjorken sum rule, are consistent with measured value of moment of the spin structure function.     

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.     

\gamma^* \gamma^* reactions at high energies

The total hadronic cross sections at high energy are calculated as a function of energy and photon virtuality in a model combining Reggeon exchange, the quark box diagram (a fixed pole in Regge language) and soft and hard pomeron exchanges evaluated in the context of dipole-dipole scattering. Good agreement is obtained with the data for the real cross section and for the real photon structure function . However the model prediction for the cross section is too small. This is attributed to an incorrect extrapolation of the dependence of the hard pomeron adopted here. Parametrising it independently shows that the hard part of the cross section can be well represented by a simple Regge pole with intercept . Received: 19 August 1999 / Published online: 3 February 2000