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arXiv 0901.2966hep-ph
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部分子能级上的单横自旋不对称性

Single Transverse Spin Asymmetries at Parton Level

H. G. Cao, J. P. Ma, H. Z. Sang

摘要:

两种因式分解方法已经提出了单一的横向自旋不对称性。一种是共线因式分解,另一种是横动量相关因式分解。它们已在强子水平上用图解展开的形式方法导出。如果这两个因式分解成立或可以被证明,那么当我们用部分子态代替强子时,它们也应该成立。我们研究这两个因子分解在部分子水平与无质量的部分子。这是不平凡的产生这些不对称性的部分子水平与无质量的部分子,因为不对称性需要螺旋翻转和非零吸收部分的散射振幅。通过用无质量部分子构造合适的部分子态,我们导出了Drell-Yan过程中不对称性的两种分解。结果表明,在部分子水平上导出的共线因式分解与在强子水平上导出的共线因式分解是不同的。我们对无质量部分子的研究结果证实了我们以前工作中对单个有质量部分子的研究结果。

英文摘要:

Two factorization approaches have been proposed for single transverse spin asymmetries. One is the collinear factorization, another is the transverse-momentum-dependent factorization. They have been previously derived in a formal way by using diagram expansion at hadron level. If the two factorizations hold or can be proven, they should also hold when we replace hadrons with parton states. We examine these two factorizations at parton level with massless partons. It is nontrivial to generate these asymmetries at parton level with massless partons because the asymmetries require helicity-flip and nonzero absorptive parts in scattering amplitudes. By constructing suitable parton states with massless partons we derive the two factorizations for the asymmetry in Drell-Yan processes. It is found from our results that the collinear factorization derived at parton level is not the same as that derived at hadron level. Our results with massless partons confirm those derived with single massive parton state in our previous works.

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