TRIUMF neutral atom trap for beta decay studies

核β衰变相关实验帮助确定了弱相互作用的性质，这是一种除了只与左手中微子进行光子耦合外，还具有大质量玻色子的理论。这样的测量仍然可以通过确定可能的新粒子的第一代轻子-夸克耦合来帮助粒子物理，但必须达到0.1%的极高精度和高意义。利用原子捕获技术，我们准备完成两组实验，达到所需的0.1%的精度。 在1毫米大小的云层中，原子核经历了β衰变，产生了三种产物：正电子、中微子和后退的子核。子核的动能很小，可以停留在一纳米的物质中，但它可以自由地逃脱陷阱。通过探测它与正电子的符合，我们可以测量中微子的动量和角分布。 我们已经学会了通过光抽运来实现37K核的自旋极化，获得了99.1+-0.1%的自旋极化。我们在测量37K原子的衰变时对其进行原子探测。我们认为这是一个重大突破，使几个新的自旋极化实验成为可能，包括反冲相对于核自旋的不对称性。 我们还将通过测量自旋为0的原子核的纯费米衰变中的β-中微子关联，来改进我们对耦合到第一代粒子的一般标量相互作用的最佳直接限制。我们正在开发的对反冲的完全角度接受将使TRIUMF EEC批准的本次实验升级中的关键系统误差降至最低，目标是达到0.1%的精度。我们将从对角关联不敏感的统计有限的运动学观测中确定这次实验的系统误差。这将是对超允许Ft测量的能量依赖性的补充，也是对pi到eNu分支比的间接限制。 一种新的可能的时间反转破坏(TRV)源产生了贝塔动量、中微子动量和有时发射的辐射伽马之间的关联。这样的实验已经在辐射克子衰变中完成，但还没有在涉及轻夸克的系统中完成。TRIUMF EEC已经批准了我们测量辐射β衰变TRV不对称性的建议，我们计划以高于0.01的精度测量，这是间接限制的一个数量级的改进。辐射β衰变的TRV不对称性，因为它们涉及伽马射线，即使在电荷变化的衰变中，也可以提供有趣的弱耦合中性电流物理。 结合原子和核技术的精密多学科实验为本科生和研究生提供了研究机会。通常，本科生的研究是关于β衰变测量所需的独立原子物理工具，而研究生则从硕士级别的仪器开始，导致完整的实验及其分析和解释。

Nuclear beta decay correlation experiments helped establish the nature of the weak interaction, a theory with massive bosons in addition to the photon coupling only to `left-handed' neutrinos. Such measurements can still assist particle physics by determining 1st-generation lepton-quark couplings of possible new particles, but must reach excellent accuracy of 0.1% with high significance. Using atom trap technology, we are poised to complete two sets of experiments reaching the 0.1% accuracy needed. Confined in a 1 mm-sized cloud, the nuclei undergo beta decay, producing three products: a positron, a neutrino, and a recoiling daughter nucleus. The daughter nucleus has very little kinetic energy and would stop in a nm of material, but it freely escapes the trap. By detecting it in coincidence with the positron, we can measure the momentum and angular distribution of the neutrino. We have learned to spin-polarize 37K nuclei by optical pumping, achieving 99.1+-0.1%. We atomically probe the 37K atoms as their decays are measured. We consider this a major breakthrough that enables several new spin-polarized experiments, including the asymmetry of recoils with respect to the nuclear spin. We also would improve our best direct limits on general scalar interactions coupling to the first generation of particles by measuring the beta-neutrino correlation in the pure Fermi decay of a spin-0 nucleus. The complete angular acceptance for recoils we are developing will minimize key systematic errors in our TRIUMF EEC-approved upgrade of this experiment, with a goal of reaching 0.1% accuracy. We would determine systematic errors for this experiment from statistics-limited kinematic observables insensitive to the angular correlation. This would be complementary to the energy dependence of superallowed Ft measurements, and to indirect constraints from the pi to e nu branching ratio. A new possible source of time-reversal violation (TRV) produces a correlation between the momenta of the beta, neutrino, and the radiative gamma sometimes emitted. Such experiments have been done in radiative kaon decay, but not in systems involving light quarks. The TRIUMF EEC has approved our proposal to measure the radiative beta decay TRV asymmetry, which we plan to measure at better than 0.01 accuracy, an order of magnitude improvement on indirect limits. Radiative beta decay TRV asymmetries, because they involve the gamma-ray, can provide access to interesting weakly coupled neutral current physics even in a charge-changing decay. Precision multidisciplinary experiments combining atomic and nuclear techniques provide research opportunities for undergrad and grad students. Typically the undergrad research is on self-contained atomic physics tools needed for the beta decay measurements, while the grad students start with masters-level instrumentation leading to a full experiment and its analysis and interpretation.