Improving spin-polarized beta-neutrino correlations

利用TRIUMF的核β衰变原子陷阱(TRINAT)，我们测量了37K下核自旋的β不对称性为-0.5706+-0.0018。我们的0.32%的精度是在原子核或中子的任何β不对称性测量中达到的最好的，并且与粒子物理标准模型的预测是一致的。 第一个β不对称性是由哥伦比亚大学的吴昌星及其合作者在1957年测量的，这是对在弱相互作用中宇称被破坏的预测的重大证实。目前人们认为宇称是完全破坏的--例如，所有已知的中微子都是“左撇子”，自旋循环与运动方向相反。为了对目前标准模型的测试有所帮助，必须达到更高的精度。 我们的测量可以用来单独约束许多新的物理，并且我们显示的约束与其他贝塔衰变测量的竞争是有利的。我们还表明，我们需要通过探测新玻色子粒子与涉及核β衰变的第一代上下夸克的耦合来补充高能物理。 我们寻求增加自旋极化及其已知的精度0.9913+-0.0009与更好的光学圆偏振光；再加上其他改进，如薄衬底反射镜(使用TRINAT项目资助)，我们将提高我们的精度在贝塔不对称性的另一个因素3-5。 我们还寻求改进真空中的离子检测仪器，以实现对单粒子中反冲核的自旋不对称性的新的和补充的实验，以及对理论修正几乎不敏感的特殊的β-反冲符合观测。相对于核自旋的反冲不对称性将具有非常高的统计数据，并有望在对某些类型的相互作用的现有β衰变测量结果的基础上，提高灵敏度一个数量级。 我们新的加拿大理科硕士。学生将为工具性硕士课程实施这一设备，这应该会导致这些实验的博士项目。两项设备将支持进一步的博士项目，升级我们世界上最好的38mK衰变中的贝塔-中微子关联测量。我们继续一次为一名本科生提供机会，帮助我们开发仪器和学习背景物理。

Using TRIUMF's atom trap for nuclear beta decay (TRINAT), we have measured the beta asymmetry with respect to the nuclear spin in 37K to be -0.5706+-0.0018. Our 0.32% accuracy is the best achieved in any beta asymmetry measurement in a nucleus or the neutron, and is in agreement with the prediction of the Standard Model of particle physics. The first beta asymmetry was measured in 1957 by C.S. Wu of Columbia University and collaborators, and was a major confirmation of the prediction that parity was violated in the weak interaction. It is presently believed that parity is completely broken-- e.g. all known neutrinos are `left-handed', with spin circulation opposite the direction of motion. To be helpful for present-day tests of the Standard Model, much better accuracy must be reached. Our measurement can be used to separately constrain much new physics, and we show constraints competing favorably with other beta decay measurements. We also show that we need improvements to complement high-energy physics by probing couplings of new boson particles to the first-generation up and down quarks involved in nuclear beta decay. We seek to increase the spin polarization and its known accuracy 0.9913+-0.0009 with better optics for the circularly polarized light; coupled with other improvements such as thin-substrate mirrors (using TRINAT project grant), we would improve our accuracy in the beta asymmetry another factor of 3-5. We also seek improvements to in-vacuum ion detection instrumentation to enable a new and complementary experiment on the spin asymmetry of the recoiling nuclei in singles, along with a particular beta-recoil coincidence observable that has very little sensitivity to theoretical corrections. The recoil asymmetry with respect to the nuclear spin would have very high statistics, and holds the promise of an order of magnitude improvement in sensitivity over existing beta decay measurements to certain types of interactions. Our new Canadian M.Sc. student would implement this equipment for an instrumental M.Sc., which should lead to a Ph.D. project on these experiments. Two equipment items would support a further Ph.D. project on the upgrade of our world-best beta-neutrino correlation measurement in unpolarized 38mK decay. We continue to provide opportunities to one undergrad at a time to help us develop the instrumentation and learn the background physics.