CAREER: Investigation of Spin Evolution in Magnetic Ultracold Neutron Bottles Used to Measure the Free Neutron Lifetime

一个孤立的中子在分裂成三个较轻的粒子之前大约能存活15分钟。这个基本过程在宇宙学中起着重要作用，它的研究补充了目前发现新物理学的努力。有两种实验室技术可以高精度地确定中子的寿命，但它们在报告值上存在显著差异。这种差异必须得到解决，以实现这些技术的潜力，以帮助探索新的物理。该奖项的研究直接支持了这一努力，通过检查磁约束的极低能量（或“超冷”）中子的行为，以确定中子寿命。该研究涉及一系列广泛的想法和技能，适合本科生参与，并将用于形成田纳西理工大学跨学科本科研究培训，指导和推广计划的核心。研究活动将与UCNTau合作项目一起进行，该项目已经建造了一个具有长的固有中子储存时间的磁引力超冷中子阱，并展示了一种探测战略，能够在洛斯阿拉莫斯国家实验室超冷中子源的一个加速器周期内进行多次高精度测量。由于在这个陷阱中的自旋演化的损失将通过开发实验的高保真自旋跟踪蒙特卡罗模拟来经验地表征，当与作为极化保持环境磁场幅度的函数的平均陷阱寿命的测量相结合时，将用于间接地表征与陷阱中的自旋演化相关的损失率，足以完成中子寿命的测量，精确到一秒。在一个专门的测试单元的测量将提供必要的信息，直接评估自旋演化的影响，在一个非常高的精度（远低于0.1%）磁阱测量的自由中子寿命。

An isolated neutron lives for about fifteen minutes before disintegrating into three lighter particles. This fundamental process plays a significant role in cosmology, and its study complements current efforts to discover new physics. Two laboratory techniques exist to determine the lifetime of a neutron with high precision, but they disagree significantly in their reported values. This discrepancy must be addressed in order to realize the potential of these techniques to help probe new physics. The research conducted with this award directly supports that effort by examining the behavior of very low energy (or "ultracold") neutrons which are magnetically confined in order to determine the neutron lifetime. The research involves a broad set of ideas and skills appropriate for undergraduate involvement and will be used to form the kernel for an interdisciplinary undergraduate research training, mentoring, and outreach program at Tennessee Technological University. Research activities will be carried out in conjunction with the UCNtau collaboration, which has constructed a magneto-gravitational ultracold neutron trap with a long intrinsic neutron storage time and demonstrated a detection strategy capable of making multiple high-precision measurements in a single accelerator cycle at the Los Alamos National Laboratory ultracold neutron source. Losses due to spin evolution in this trap will be empirically characterized by developing a high-fidelity spin-tracking Monte Carlo simulation of the experiment which, when combined with measurements of the mean trap lifetime as a function of the polarization-preserving ambient magnetic field magnitude, will be used to characterize indirectly the loss rate associated with spin evolution in the trap, sufficient for completing measurement of the neutron lifetime to an accuracy of one second. Measurements in a dedicated test cell will provide information necessary to assess directly the effect of spin evolution in a very high-precision (well below 0.1%) magnetic trap measurement of the free neutron lifetime.