Møller旋光法中磁化铁箔和镍箔中电子自旋极化的精确测定
Accurate Determination of the Electron Spin Polarization In Magnetized Iron and Nickel Foils for Møller Polarimetry
摘要：
位于弗吉尼亚州纽波特纽斯市杰斐逊实验室A厅的Møller偏振计在过去二十年中提供了可靠的电子束偏振测量，达到了通常要求的绝对不确定度的$\pm$ 1\%水平。然而，即将提出的实验计划，包括MOLLER和SoLID有严格的要求，在0.4\%的水平\cite{MOLLER2014, SoLID2019}的光束偏振测量精度，需要系统地重新检查的所有贡献的不确定性。Møller偏振测量法使用极化电子束在具有极化原子电子的目标上的双极化散射不对称性。目标是一种磁化的铁磁材料，以使自旋在给定方向上对齐。在A厅中，靶是垂直于射束排列的纯铁箔，并且在平行于或反平行于射束方向的平面外磁化。检测器的验收设计为在分析功率最大（-7/9）的质心坐标系中收集接近90 $^{\circ}$的散射电子。主要的系统误差之一来自于目标箔偏振的确定。磁饱和靶箔的极化需要饱和磁化强度和$g^\prime$的知识，电子$g$因子包括来自自旋和轨道角动量的分量，从自旋和轨道角动量确定磁化的自旋分数。本文利用现有的世界数据提供了一个最好的估计目标极化的镍和铁箔，包括不确定性的磁化，高场和温度的依赖性，以及部分贡献的磁化轨道效应。在294 K下，铁的薄膜电子自旋极化率为0.08020 $\pm$ 0.00018（@4 T外加场），镍的薄膜电子自旋极化率为0.018845 $\pm0.000053$（@2 T外加场）.
英文摘要：
The Møller polarimeter in Hall A at Jefferson Lab in Newport News, VA, has provided reliable measurements of electron beam polarization for the past two decades reaching the typically required $\pm$1\% level of absolute uncertainty. However, the upcoming proposed experimental program including MOLLER and SoLID have stringent requirements on beam polarimetry precision at the level of 0.4\% \cite{MOLLER2014, SoLID2019}, requiring a systematic re-examination of all the contributing uncertainties. Møller polarimetry uses the double polarized scattering asymmetry of a polarized electron beam on a target with polarized atomic electrons. The target is a ferromagnetic material magnetized to align the spins in a given direction. In Hall A, the target is a pure iron foil aligned perpendicular to the beam and magnetized out of plane parallel or antiparallel to the beam direction. The acceptance of the detector is engineered to collect scattered electrons close to 90$^{\circ}$ in the center of mass frame where the analyzing power is a maximum (-7/9). One of the leading systematic errors comes from determination of the target foil polarization. Polarization of a magnetically saturated target foil requires knowledge of both the saturation magnetization and $g^\prime$, the electron $g$-factor which includes components from both spin and orbital angular momentum from which the spin fraction of magnetization is determined. This paper utilizes the existing world data to provide a best estimate for target polarization for both nickel and iron foils including uncertainties in magnetization, high-field and temperature dependence, and fractional contribution to magnetization from orbital effects. We determine the foil electron spin polarization at 294~K to be 0.08020$\pm$0.00018 (@4~T applied field) for iron and 0.018845$\pm0.000053$ (@2~T applied field) for nickel.
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