Accurate Electron Spin Optical Polarimetry

该奖项资助的工作将有助于提高美国和国际上大型电子加速器所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20世纪中叶，科学家们还认为，在实验室和实验室的完美镜像中，自然界都会以完全相同的方式工作。换句话说，通过做任何人们能想象到的物理实验，一个人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。这个想法被实验证明是不正确的，这些实验“破坏了宇称”，只产生了速度和自旋指向相反方向的‘左撇子’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，就像玩具陀螺的自转一样，必须以极高的灵敏度测定，无论是在产生电子的低能时，还是在它们被加速到非常接近光速的高能时。这项工作的目的是用一种新的方法测量低能下的自旋，使用精确的电子自旋光学偏振方法(伊索)。伊索方法的精确度已被证明约为1.5%，现在将进行改进，以提供比0.5%更好的精确度。因此，它将极大地提高新一代宇称破坏实验提供的信息的质量。这反过来将产生对弱电的更好的理解，弱电是自然界的三种基本力量之一。伊索技术是由该研究小组在NSF资助的以前的工作中发明和开发的，该技术基于对电子激发的原子的荧光的偏振测量，电子的平均自旋将被确定。它提供了电子自旋极化的绝对测量，不需要为校准而进行动态过程的理论计算。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，极化在这个宽度上变化。这项技术以前被用来测量电子束极化，精度在1%到1.5%之间。研究小组现在提议设计和建造一个伊索系统，作为概念的证明，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。研究团队希望证明重复和可靠的电子光学偏振测量精度优于0.5%，这是将加速器注入器上使用的Mott偏振测量仪校准到0.5%精度所必需的。下一代电弱宇称破坏实验将需要这样的Mott精度。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)和美因策Mikrotron(MAMI)的注入器小组一起制定一项协议，以便在一个或两个加速器上安装伊索设施。

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.