手征有效场论中质子自旋及其它八重态重子轴荷的研究

发布时间：2018-09-18 19:43

【摘要】：继1988年EMC在极化深度非弹性散射实验中测量质子中的夸克自旋贡献几乎为零,CERN,DESY,JLab,RHIC和SLAC亦对质子自旋结构进行了相关的测量,测量结果显示,核子味态轴荷0a(被解释为质子中夸克的自旋贡献)在能标为3Ge V2时,大约为0.35。尽管这与EMC的测量结果不同,但相对于早期的夸克模型此测量值依旧很小。在静态夸克模型下,夸克贡献了质子的全部自旋;在相对论夸克模型中,夸克贡献质子60%的自旋,另外40%则转变为夸克的角动量。那么夸克“丢失”的自旋哪里去了呢?这也被称为自旋危机或自旋困惑,这也激起了理论界和实验界至今近三十年对质子自旋内部结构的研究。对于理解质子纵向自旋结构,理论上对解释自旋困惑做出了很多努力。例如,核子的π介子云以及单胶子交换作用将自旋转化为轨道角动量,QCD胶子修正,奇异夸克贡献,八重态轴荷8a的SU(3)破缺等。目前的实验数据指向质子自旋困惑是价夸克效应,价夸克对单态轴荷0a的贡献几乎充满了测量值。奇异夸克和QCD胶子修正对单态轴荷的贡献非常小,不足以解释自旋困惑。在深度非弹性散射实验中,解释观测结构函数的理论基础是QCD。QCD在夸克质量为零的极限下,具有手征对称性。手征有效场论是QCD的低能有效理论,基态手征对称性破缺产生Goldstone玻色子,作为手征有效理论的有效介子场。吸收和发射虚介子对描述强子的性质起到至关重要的作用。手征有效场论与一般的唯象模型不同,它是一个比较系统的理论,基于与QCD相同的手征对称性,在强子物理的研究中有着广泛的应用,对研究强子谱与强子结构有很多成功的应用。考虑QCD演化的一般性质可以得出这样的结论,与QCD夸克模型相匹配的自然标度非常低,所以质子的大部分动量由价夸克携带,胶子可以认为在理论中被积掉。Jaffe(1987)提出了这样的方案,实验测量的质子自旋值小,是因为实验测量的能标与夸克模型给出结果的能标不同。因此我们用有效场论研究质子的自旋,以及其它八重态重子的轴荷。我们在计算中使用了finite-range正规化方法,比传统的正规化方法更具优势。在计算中我们包括了八重态和十重态重子中间态,这丰富了核子和重子的自旋和味结构,在手征对称性的约束下重新分配了自旋。单胶子交换(OGE)效应,虽然不属于手征有效场论的范畴,但对于自旋依赖的物理量起着非常重要的作用,所以我们在计算中也包括了OGE换效应。我们分别计算了各夸克的自旋贡献,所以可以同时得到单态轴荷0a和非单态轴荷a_3(g_A),a_8。对于质子自旋的解释,我们的计算同时给出三个轴荷的合理值,与实验吻合地非常好,优于其它模型,其它模型只部分的给出某些轴荷的合理解释。下面列出对质子计算得到的主要结论:1、通过取实验测量值a_3=1.27,拟合出我们计算中唯一的一个参数,低能自旋常数S_q~0.88q s,这个常数体现了相对论和禁闭效应的大小,小于传统夸克模型(不考虑相对论效应)值,大于以往的极端相对论效应~0.65,将夸克的自旋转化为轨道角动量。我们计算中参数极少,优于其它模型,体现了计算的可靠性。我们利用此参数对a_8,a_0进行计算。2、计算得到与实验中超子β衰变SU(3)假设下的测量值~0.58非常一致。3、对于单态轴荷a_0,我们给出适用于夸克模型的低能标处夸克自旋贡献a_0~0.55及夸克分布?u~0.91,?d~-0.36,?s~-0.01。由相对论效应、介子云以及OGE修正,质子的夸克自旋贡献由初始夸克模型贡献全部变为贡献大约一半。4、由于单态轴矢流的反常维度不为零,使得单态轴荷0a是标度依赖的,通过适当的演化,得到的实验能标处的结果与实验测量值~0.35符合地非常好。演化模型在我们的计算前仅是给出了定性的分析(Jaffe1987),我们的计算给出了精确的定量描述,很好的解释了质子困惑。5、对于奇异夸克自旋的贡献,我们得到的结果为负值,大小约为0.01。与实验测量吻合的很好。我们的计算对理解质子困惑提供了非常重要的深入的认识。介子云,OGE效应及相对论效应等将夸克的自旋转化为轨道角动量,并经过演化得到实验测量值。我们的计算直接给出各味道夸克的自旋贡献,增加了对质子内部结构的认识。同时,在我们的计算中变动介子强子耦合常数D,F,C,及截断函数的形式,给出的结果皆在我们估算的误差范围内,说明了计算的稳定性。我们采用与计算质子自旋相同的办法计算了其它八重态重子的自旋和轴荷。计算中使用了质子中拟合的低能自旋常数s_q,不再有其它参数。我们计算的同位旋矢量轴荷,与其它理论计算以及格点数据非常接近,这说明我们计算的结果是合理的。我们对八重态轴荷8a进行了计算,.。对于八重态重子的自旋Σ与质子得到的结果相似,在低能标处,夸克自旋贡献大概为价夸克区域的50(25)60%,演化到实验能标3 Ge V~2,得到-0.35。对于八重态重子的各味夸克自旋贡献,与质子类似,价夸克(Σ、(?)中u、s夸克)中提供了重子自旋的主要贡献,海夸克(Σ、(?)中d夸克)提供的贡献很小~0.01-0.02,自旋方向与重子自旋方向相反。
[Abstract]:Further to the 1988 EMC polarization-depth inelastic scattering experiment, which measured almost zero quark spin contributions in protons, CERN, DESY, JLab, RHIC and SLAC also measured the spin structures of protons. The measurements show that the nuclear flavor state axial charge 0A (interpreted as quark spin contributions in protons) is about 0.35% at the energy scale of 3 Ge V2. Although this is different from the EMC measurements, it is still very small compared to the earlier quark models. In the static quark model, quarks contribute all the spins of protons; in the relativistic quark model, quarks contribute 60% of the spins of protons and 40% of the angular momentum of quarks. What about spin crisis or spin perplexity? This has also sparked theoretical and experimental studies of the internal structure of proton spin in the last 30 years. Orbital angular momentum, QCD gluon correction, singular quark contribution, SU (3) breakage of octet axial load 8a, etc. The present experimental data indicate that the proton spin puzzle is the valence quark effect, and the valence quark contribution to the singlet axial load 0A is almost full of measured values. In deep inelastic scattering experiments, the theoretical basis for explaining the observed structure function is the chiral symmetry of QCD.QCD at the limit of zero quark mass.Chiral effective field theory is the low-efficiency theory of QCD.Chiral chiral symmetry breaking produces Goldstone bosons as an effective meson field of chiral effective theory.Absorption and emission Virtual mesons play an important role in describing the properties of hadrons. Chiral effective field theory, unlike the general phenomenological model, is a relatively systematic theory. Based on the same chiral symmetry as QCD, it is widely used in hadronic physics and has many successful applications in the study of hadronic spectra and hadronic structures. The general nature of evolution leads to the conclusion that the natural scales matching the QCD quark model are very low, so most of the proton momentum is carried by valence quarks, and gluons can be thought to have been accumulated in theory. The model gives different energy scales. Therefore, we study the spin of protons and the axial loads of other octet baryons by using the effective field theory. The spin and taste structures of baryons are redistributed under the constraint of chiral symmetry. The single gluon exchange (OGE) effect, though not in the chiral effective field theory, plays a very important role in spin-dependent physical quantities, so we also include the OGE exchange effect in our calculations. We have calculated the spins of each quark separately. The spin contribution, therefore, can be obtained both singlet and non-singlet axial loads a_3 (g_A), a_8. For the explanation of proton spin, our calculation gives three reasonable values of axial loads at the same time, which are in good agreement with the experiment and are superior to other models. Other models only give some reasonable explanations of axial loads. The following is a list for proton calculations. The main conclusions are a s follows: 1. By taking the experimental value a_3=1.27, the only parameter in our calculation is fitted. The low-energy spin constant S_q~0.88q s, which reflects the magnitude of relativity and confinement effect, is smaller than the traditional quark model (without considering relativistic effect), and is larger than the extreme relativistic effect ~0.65. We use this parameter to calculate a_8, a_0, and the calculated values are very consistent with the experimental values of ~0.58 under the assumption of superon beta decay SU(3). 3. For the singlet axial load a_0, we give a low energy scale suitable for the quark model. Quark spin contribution a_0~0.55 and quark distribution u~0.91,? D~-0.36,? S~-0.01. By relativistic effect, meson cloud and OGE modification, the contribution of quark spin of proton is changed from the initial quark model contribution to about half of the contribution. 4. Because the anomalous dimension of the single state axial vector current is not zero, the singlet axial load 0A is scale-dependent, and through appropriate modification Evolution model only gives qualitative analysis before our calculation (Jaffe 1987). Our calculation gives a precise quantitative description, which explains the proton puzzle very well. 5. For the contribution of the singular quark spin, our results are negative. Our calculations provide a very important insight into the proton puzzle. Mesoon clouds, OGE effects and relativistic effects transform the quark's spin into orbital angular momentum, and the experimental values are obtained by evolution. Our calculations directly give the spins of quarks of various flavors. Meanwhile, in our calculation, we change the form of hadronic coupling constants D, F, C, and truncation function. The results are all within the error range of our estimation, which shows the stability of the calculation. Spin and axial load. The low-energy spin constant s_q fitted in the proton is used in the calculation, and there are no other parameters. The isospin vector axial load calculated by us is very close to other theoretical calculations and the lattice data, which shows that our calculation results are reasonable. We have calculated the octet axial load 8a,... For the baryon of the octet state. Spin_is similar to that obtained by protons. At low energy scales, the contribution of quark spin is about 50(25)60% of the valence quark region, and evolves to the experimental energy scales 3 Ge V~2, resulting in -0.35. The contribution of the middle D quark is very small ~0.01-0.02, and the spin direction is opposite to the baryon spin direction.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O572.33

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