Accurate Electron Spin Optical Polarimetry

该奖项资助的工作将有助于提高在美国和国际上的大型电子加速器上进行的电子自旋测量的准确性。自旋是电子的一种内在属性，它决定了电子的大部分行为。 直到世纪中期，科学家们还认为，自然界在实验室和实验室的完美镜像中都以完全相同的方式工作。 换句话说，通过做任何一个可以想象的物理实验，你将无法分辨他或她是在一个实验室还是在它的“镜子”等价物中。 这个想法被“违反宇称”的实验证明是不正确的，只产生速度和自旋指向相反方向的“左手”电子。 今天，这些实验已经变得越来越复杂，以至于电子的平均自旋，类似于玩具陀螺的自旋，必须以极高的灵敏度来确定，无论是在低能量下，当它们产生时，还是在高能量下，当它们被加速到非常接近光速时。本工作的目的是用一种新的方法，即精确电子自旋光学偏振测量法（AESOP）来测量低能自旋。 AESOP方法已被证明精度约为1.5%，现在将被改进，以提供优于0.5%的精度。 因此，它将大大提高新一代奇偶违反实验提供的信息质量。 这反过来又会使我们更好地理解自然界三种基本力之一的电弱力。AESOP技术是由该研究小组在NSF资助的先前工作中发明和开发的，该技术基于测量由平均自旋待确定的电子激发的原子荧光后的光偏振。 它提供了一个绝对测量电子自旋极化，不需要理论计算的动态过程进行校准。然而，它确实有潜在的系统误差，特别是如果正在研究的电子束具有广泛的能量分布，并且在该宽度上变化的极化。这种技术以前曾用于测量电子束偏振，精度在1%和1.5%之间。研究小组现在建议设计和建造一个AESOP系统，作为概念验证，该系统将允许详细研究该方法的潜在系统误差，并展示如何消除或最大限度地减少此类误差。研究小组希望能够以优于0.5%的精度证明重复和可靠的电子光学偏振测量，这是校准加速器注入器使用的Mott偏振计所需的，精度为0.5%。 这样的莫特精度将需要下一代的电弱宇称破坏实验。作为该项目的一部分，将与托马斯杰斐逊国家加速器设施（JLab）和Mainzer Mikrotron（MAMI）的注射器组一起制定一项协议，以便在一个或两个加速器上安装AESOP设施。

This award funds work that will help improve the accuracy of electron spin measurements done at large electron accelerators both in the United States and internationally. Spin is an intrinsic property of the electron that determines much of its behavior. Until the middle of the 20th century, scientists believed that nature would work in exactly the same way in both a laboratory and a perfect mirror image of that laboratory. In other words, by doing any physics experiment that one could imagine, one wouldn't be able to tell whether he or she was in one laboratory or its "looking glass" equivalent. This idea was shown to be incorrect by experiments that "violated parity," producing only electrons that were 'left-handed' with their velocities and spins pointing in opposite directions. Today, these experiments have become increasingly sophisticated, such that the average spin of the electrons, analogous to the spin of toy tops, must be determined with exquisite sensitivity, both at low energy, when they are produced, and at high energy after they have been accelerated to speeds very close to that of light. The goal of this work is to measure the spins at low energy in a new way, using the method of Accurate Electron Spin Optical Polarimetry (AESOP). The AESOP method has been proven to accuracies of about 1.5%, and will now be refined to provide accuracies better that 0.5%. As such, it will greatly increase the quality of the information being provided by a new generation of parity violation experiments. This in turn will yield an even better understanding of the electroweak force, one of the three fundamental forces of nature. The AESOP technique, based on the measurement of light polarization following the fluorescence of atoms excited by the electrons whose average spin is to be determined, was invented and developed by this research team in previous work funded by the NSF. It provides an absolute measurement of electron spin polarization that does not require theoretical calculations of dynamic processes for calibration. It does, however, have potential systematic errors, especially if the electron beam being studied has a broad energy spread with a polarization that varies across this width. This technique has previously been used to measure electron beam polarization with an accuracy of between 1% and 1.5%. The research team now proposes to design and build, as a proof of concept, an AESOP system that will allow for a detailed study of the method's potential systematic errors and show how to eliminate or minimize such errors. The research team expects to demonstrate repeated and reliable electron optical polarimetric measurements with better than 0.5% accuracy, which is needed to calibrate Mott polarimeters used at accelerator injectors to an accuracy of 0.5%. Such Mott accuracy will be required for the next generation of electro-weak parity violation experiments. As part of this project, a protocol will be developed with the injector groups at the Thomas Jefferson National Accelerator Facility (JLab) and the Mainzer Mikrotron (MAMI) for installing an AESOP facility at one or both accelerators.