arXiv 1503.022502015-03hep-ph

核子自旋结构

Nucleon spin structure

Wei Zhu, Jianhong Ruan

备注：: 46 pages. 26 figures
发表信息：: International Journal of Modern Physics E Vol. 24, No. 10 (2015) 1550077

摘要：

本文在简单的核子图象中讨论了核子的自旋结构，包括三个部分：（1）利用一个非线性QCD演化方程--带部分子复合修正的DGCD方程，从低尺度出发，动态地预言了质子中极化胶子的分布，其中核子几乎只由价夸克组成。我们发现胶子极化对核子自旋结构的贡献比大多数其他理论的预测要大得多。这一结果表明，胶子的轨道角动量的平衡胶子自旋动量是必要的;（ii）质子的自旋结构函数$g_1^p$的研究，其中部分子分布的微扰演化和非微扰矢量介子优势（VMD）模型。我们预测小$x$时从较低$Q^2$到较高$Q^2$的$g_1^p$渐近行为。结果是兼容的数据，包括HERA早期估计和COMPASS新的结果;（iii）广义Gerasimov-Drell-Hearn（GDH）总和规则的基础上理解的极化部分子分布的质子具有较高的扭曲贡献。提出了一个简单的参数化公式，以清楚地表示质子中不同组分对$Γ_1^p(Q^2)$的贡献。结果表明质子内部可能存在一个大小为$0.2-0.3~ fm$的扩展天体。

英文摘要：

This paper contains three parts relating to the nucleon spin structure in a simple picture of the nucleon: (i) The polarized gluon distribution in the proton is dynamically predicted starting from a low scale by using a nonlinear QCD evolution equation-the DGLAP equation with the parton recombination corrections, where the nucleon is almost only consisted of valence quarks. We find that the contribution of the gluon polarization to the nucleon spin structure is much larger than the predictions of most other theories. This result suggests a significant orbital angular momentum of the gluons is required to balance the gluon spin momentum; (ii) The spin structure function $g_1^p$ of the proton is studied, where the perturbative evolution of parton distributions and nonperturbative Vector Meson Dominance (VMD) model are used. We predict $g_1^p$ asymptotic behavior at small $x$ from lower $Q^2$ to higher $Q^2$. The results are compatible with the data including the HERA early estimations and COMPASS new results; (iii) The generalized Gerasimov-Drell-Hearn (GDH) sum rule is understood based on the polarized parton distributions of the proton with the higher twist contributions. A simple parameterized formula is proposed to clearly present the contributions of different components in the proton to $Γ_1^p(Q^2)$. The results suggest a possible extended objects with size $0.2-0.3~ fm$ inside the proton.

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