GeV =200时极化p+p碰撞中非常正向中子产生的包含截面和单横自旋不对称性
Inclusive cross section and single-transverse-spin asymmetry for very forward neutron production in polarized p+p collisions at sqrt(s)=200 GeV
摘要：
在RHIC PHENIX实验中，测量了sqrt（s）=200 GeV极化p+p碰撞中，单横自旋不对称性A_N和非常前向角中子产生的截面的能量依赖关系。中子在前向探测器中观察到，覆盖的角度范围高达2.2 mrad。我们报告的结果与中子的动量分数x_F=0.45至1.0。测量的截面的能量依赖性与x_F标度是一致的，与ISR实验测量的在sqrt（s）=30.6- 62.7 GeV的非极化p+p碰撞中的中子产生相比较。用π交换机制描述了p+p碰撞和HERA测量的e+p碰撞中产生大x_F中子的截面。观测到的前向中子不对称性很大，当x_F=0.8时，达到A_N=-0.08+/-0.02;当x_F为负时，测量到的后向不对称性与零一致。所观察到的不对称性的正向中子生产的π交换框架内进行了讨论，由于π交换和nonflip振幅从所有Reggeon交换自旋翻转振幅之间的干扰。在π交换描述，测量的中子不对称性是敏感的其他雷金交换的贡献，即使是小幅度。
英文摘要：
The energy dependence of the single-transverse-spin asymmetry, A_N, and the cross section for neutron production at very forward angles were measured in the PHENIX experiment at RHIC for polarized p+p collisions at sqrt(s)=200 GeV. The neutrons were observed in forward detectors covering an angular range of up to 2.2 mrad. We report results for neutrons with momentum fraction of x_F=0.45 to 1.0. The energy dependence of the measured cross sections were consistent with x_F scaling, compared to measurements by an ISR experiment which measured neutron production in unpolarized p+p collisions at sqrt(s)=30.6--62.7 GeV. The cross sections for large x_F neutron production for p+p collisions, as well as those in e+p collisions measured at HERA, are described by a pion exchange mechanism. The observed forward neutron asymmetries were large, reaching A_N=-0.08+/-0.02 for x_F=0.8; the measured backward asymmetries, for negative x_F, were consistent with zero. The observed asymmetry for forward neutron production is discussed within the pion exchange framework, with interference between the spin-flip amplitude due to the pion exchange and nonflip amplitudes from all Reggeon exchanges. Within the pion exchange description, the measured neutron asymmetry is sensitive to the contribution of other Reggeon exchanges even for small amplitudes.
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