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

这个建议解决了我们在确定衰变核的自旋极化度时的最大系统误差。我们需要更高的精度来改进我们的TRIUMF中性原子阱（TRINAT）计划，以便我们对衰变相关性的标准模型预测的测试与其他改进粒子物理实验保持竞争力和互补性。 我们想直接测量通过光学泵浦钾原子获得的自旋极化度。最直接的方法是首先分裂我们原子能级的自旋投影能量-使用外部磁场，塞曼效应-然后用共振激光扫描它们，激发原子中的光学跃迁。然而，当我们通过光泵浦自旋跃迁时，我们必须几乎均匀地激发所有这些子能级，所以我们必须保持能量分裂远低于我们的光泵浦跃迁的自然线宽（技术上，6 MHz宽的4S到4P 1/2 770 nm跃迁）。因此，在RTI的建议下，我们将使用405 nm处的窄线宽1.1 MHz 4S到5 P共振跃迁来解决塞曼分裂原子子能级。测量的相对群体将给我们一个直接的模型无关的核极化测量，我们目前不太直接的测定，因为我们试图提高我们的精度优于0.1%的关键测试。 进一步的未来研究应用，使我们的激光冷却钾原子云大大更冷，更小，也描述了，沿着与我们的精度测量的潜在影响，通过提高我们的衰变产物之间的角度分辨率。 我已经指导了两个连续的合作研究项目，与耐心的学生一起试图使这种新方法与过时的第一代商用405 nm激光器一起工作。在完成简单得多的测量的同时，我们发现了几个问题，这些问题使得这些棘手的测量无法用现有的设备进行。这个RTI将升级到一个更好的模型405 nm激光器，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，可用于均匀探测整个原子系综。 它将被一个现有的加拿大博士使用。论文学生的自旋极化实验，沿着的帮助下，从PI。这将有望成为通过TRIUMF学生计划的一到三个本科生合作研究项目的基础（所有广告都邀请所有人申请，我们很感激一些学生在他们的封面上感谢我们），因为我们考虑到从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研究项目一样，即使没有实验室课程（在较小的大学并不总是可用），也可以由2A学生完成，所有的求职信当然都由PI阅读。

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.