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解成三个较轻的粒子之前大约能存活15分钟。这一基本过程在宇宙学中扮演着重要的角色，对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，但它们所报告的值有很大的不同。为了实现这些技术帮助探索新物理学的潜力，必须解决这种差异。该奖项的研究直接支持了这一努力，通过检查极低能量（或“超冷”）中子的行为，这些中子被磁限制，以确定中子的寿命。这项研究涉及广泛的思想和技能，适合本科生的参与，并将被用来形成田纳西理工大学跨学科本科生研究培训、指导和推广计划的核心。研究活动将与UCNtau合作进行，该合作已经构建了一个具有长内在中子储存时间的磁引力超冷中子阱，并展示了一种能够在洛斯阿拉莫斯国家实验室超冷中子源的单个加速器周期内进行多次高精度测量的探测策略。通过开发高保真的自旋跟踪蒙特卡罗实验模拟，将该实验与作为保持极化的环境磁场大小的函数的平均阱寿命的测量相结合，将用于间接表征与阱中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。在专用测试单元中的测量将提供必要的信息，以直接评估在非常高精度（远低于0.1%）的自由中子寿命磁阱测量中自旋演化的影响。

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.