Twist-3 formalism for single transverse spin asymmetry reexamined: Semi-inclusive deep inelastic scattering
Twist-3 formalism for single transverse spin asymmetry reexamined: Semi-inclusive deep inelastic scattering
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DOI：
10.1016/j.nuclphysb.2006.11.016
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发表时间：
2006-10
期刊：
影响因子：
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通讯作者：
H. Eguchi;Y. Koike;Kazuhiro Tanaka
中科院分区：
文献类型：
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作者：
H. Eguchi;Y. Koike;Kazuhiro Tanaka
在共线分解的框架下，研究了半包容深度非弹性散射ep↑→π x中介子产生的单自旋不对称性。我们推导了横向极化核子的扭曲-3夸克-胶子相关函数的完整截面公式，包括所有类型的极（硬极、软费米子-极和软胶子-极）贡献，这些贡献产生了SSA所需的强相互作用相。我们证明了每个极点贡献的部分硬部满足Ward恒等式中色规不变性的某些约束。我们证明了这些新约束的使用对于将费曼图的共线展开重组为明显的规范不变形式是至关重要的，从而可以得到不重复计数的扭曲-3分布的完整集合的截面分解公式。它还为实际计算提供了一种更简单的方法。我们还基于我们的横截面公式给出了一个简单的SSA估计，使用了一个代表相关的扭曲-3夸克-胶子相关的“软胶子-极函数”模型，并比较了涉及软胶子-极函数导数的项与“非导数”项的大小。
We study the single spin asymmetry (SSA) for the pion production in semi-inclusive deep inelastic scattering, ep↑→eπX, in the framework of the collinear factorization. We derive the complete cross section formula associated with the twist-3 quark–gluon correlation functions for the transversely polarized nucleon, including all types of pole (hard-pole, soft-fermion-pole and soft-gluon-pole) contributions which produce the strong interaction phase necessary for SSA. We prove that the partonic hard part from each pole contribution satisfies certain constraints from Ward identities for color gauge invariance. We demonstrate that the use of these new constraints is crucial to reorganize the collinear expansion of the Feynman diagrams into manifestly gauge-invariant form so as to obtain the factorization formula for the cross section in terms of a complete set of the twist-3 distributions without any double counting. It also provides a simpler method for the actual calculation. We also present a simple estimate of SSA based on our cross section formula, using a model for the “soft-gluon-pole function” that represents the relevant twist-3 quark–gluon correlation, and compare the magnitude of the terms involving the derivative of the soft-gluon-pole function with that of the “nonderivative” terms.