Direct measurement of nuclear polarization for decay correlations testing the Standard Model

这一建议解决了我们在确定衰变原子核的自旋极化程度方面存在的最大系统误差。我们需要更高的精度来改进我们的TRIUMF中性原子陷阱(TRINAT)程序的大部分，以便我们对衰变关联的标准模型预测的测试保持与其他改进的粒子物理实验的竞争和补充。我们想通过光学泵浦我们的钾原子来直接测量我们达到的自旋极化程度。要做到这一点，最直接的方法是首先分割原子能级的自旋投影--使用外部磁场，即塞曼效应--然后用共振激光扫描它们，激发原子的光学跃迁。然而，当我们通过光抽运使这些子能级自旋偏振时，我们必须几乎均匀地激发它们，所以我们必须将能量分裂保持在我们的光泵浦跃迁(从技术上讲，6 MHz宽的4S到4P1/2770 nm跃迁)的自然线宽以下。因此，在这个RTI方案中，我们将使用较窄的线宽1.1 MHz 4S到5P在405 nm处的共振跃迁来解析塞曼分裂原子的子能级。测量的相对人口将给我们一个直接的与模型无关的核极化测量，这是对我们目前不那么直接的确定的关键考验，因为我们寻求将我们的精度提高到0.1%以上。还描述了未来的进一步研究应用，使我们的激光冷却的钾原子云大大变得更冷和更小，以及它通过提高我们衰变产品之间的角度分辨率对我们的精确测量的潜在影响。我已经指导了两个连续的合作研究术语，学生们试图让这种新方法与过时的第一代商业激光器一起工作，波长为405 nm。在完成简单得多的测量的同时，我们已经确定了几个问题，这些问题使得这些棘手的测量在目前的设备上是不可行的。这种RTI将升级到更好的405 nm激光模型，具有指定的更窄的线宽、更好的空间模式质量和足够的功率来统一探测整个原子系综。它将被一名现有的加拿大博士论文学生用于自旋极化实验，并得到P.I.的帮助。它有望成为TRIUMF学生项目一到三个本科生合作研究条款的基础(所有广告都邀请所有人申请，我们很感激一些学生在封面上感谢我们)，因为我们考虑从2021年夏天开始的实践教程的安全性和可能的大流行状态。这些，就像我们大约一半的本科生研究项目一样，即使没有实验室课程，也可以由一个2A年级的学生完成(在规模较小的大学并不总是可用的)，所有的求职信当然都是由PI阅读的。

This proposal addresses our largest systematic errors in determining the degree of spin polarization of our decaying nuclei. We need more accuracy to improve most of our TRIUMF neutral atom trap (TRINAT) program, so that our tests of the Standard Model predictions of decay correlations remain competitive with and complementary to other improving particle physics experiments.  We want to measure directly the degree of spin polarization we achieve by optically pumping our potassium atoms. The most direct way to do that is to first split the spin projections of our atomic levels in energy-- using an external magnetic field, the Zeeman effect-- and then scan over them with a resonant laser, exciting an optical transition in the atom. However, we must excite all these sublevels nearly uniformly when we spin-polarize them by optical pumping, so we must keep the energy splitting well below the natural linewidth of our optical pumping transition (technically, the 6 MHz-wide 4S to 4P1/2 770 nm transition). So with this RTI proposal we would resolve the Zeeman-split atom sublevels using the narrower-linewidth 1.1 MHz 4S to 5P resonant transition at 405 nm. The measured relative populations would give us a direct model-independent nuclear polarization measurement, a critical test of our present less direct determination as we seek to improve our accuracy to better than 0.1%.   A further future research application, making our laser-cooled potassium atom cloud substantially colder and smaller, is also described, along with its potential impacts on our precision measurements by improving the angle resolution between our decay products.   I have guided two successive co-op research terms with patient students trying to make this new approach work with an obsolete first-generation commercial laser at 405 nm. While completing much simpler measurements, we've identified several issues that make these tricky measurements unfeasible with present equipment. This RTI would upgrade to a much better model 405 nm laser with specified narrower linewidth, better spatial mode quality, and sufficient power available to uniformly probe the entire atomic ensemble.   It would be used by an existing Canadian Ph.D. thesis student for the spin-polarized experiments, along with help from the P.I. It would hopefully be the basis of one to three undergrad co-op research terms through the TRIUMF student program (all ads invite all to apply, and we are grateful some students thank us for that in their cover), as we consider safety of hands-on tutorials starting summer 2021 and possible pandemic status. These, like roughly half our undergrad research projects, could be done by a year 2A student even without the lab courses (not always available at smaller universities), and all cover letters are of course read by the PI.