Characterization of Systematic Effects in Ultracold Neutron Tests of Fundamental Symmetries

最成功和研究最多的物理理论之一是标准模型（SM），它描述了宇宙如何在非常小的尺度上运作。在过去的五十年里，这一模式已经以多种不同的方式得到了验证。原则上，这样的基本理论应该能够预测大尺度下的宇宙观测，但在许多值得注意的情况下，它未能做到这一点。这表明了一种令人兴奋的可能性，即宇宙中存在着我们不知道的基本特征。由于这些未知的性质迄今为止一直无法被发现，发现它们需要具有新的灵敏度的实验，需要创新的方法。两个这样的实验利用了最近在产生极低能量“超冷”中子方面的进展。它们是UCNTau，测量自由中子衰变所需的平均时间，和nEDM，测量孤立中子中的电荷分布。该项目的重点是开发三种旨在提高这些实验灵敏度的技术。研究工作将组建一个跨学科的团队，以加强科学与技术之间的协同作用，并将针对早期的本科生和大学预科生，以更有效地将实际研究经验与学生的学术工作联系起来。确定的磁场映射的UCNτ Halbach阵列和从头计算模拟加载的超冷中子（UCN）相空间分布到一个半经典的自旋跟踪蒙特卡罗模型，开发的空间和自旋自由度之间的纠缠。这一目标将确保与自旋动力学（去极化）相关的系统效应的表征与统计精度的预期改进保持同步。第二个核心活动是为UCNτ工作开发一个实时监控器，该监控器将对去极化速率设置逐次运行的经验限制，并作为计算模型的交叉检查。第三个目标是开发一种量子传感器，基于金刚石中的氮空位缺陷，优化以帮助控制和表征nEDM实验的磁场和电场，该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的评估被认为值得支持。影响审查标准。

One of the most-successful and best-studied physical theories is the Standard Model (SM), which describes how the universe functions at very small scales. This model has been verified in many different ways over the course of five decades. In principle, such a fundamental theory should be able to predict observations about the universe at large scales, but in a number of notable cases it fails to do so. This suggests an exciting possibility, that there are fundamental features about the universe of which we are unaware. Since these unknown properties have so far evaded detection, discovering them requires experiments with a new level of sensitivity, requiring innovative approaches. Two such experiments leverage recent progress in the production of very low energy “ultracold” neutrons. They are UCNtau, which measures the average time required for a free neutron to decay, and nEDM, a measurement of the charge distribution in an isolated neutron. This project focuses on the development of three techniques designed to enhance the sensitivity of these experiments. The research effort will assemble a cross-disciplinary team to strengthen the synergy between science and technology and will target early undergraduates and pre-college students to more effectively connect practical research experience with the students’ academic work.The first of three primary research activities to be carried out in this project is the inclusion of empirically-determined magnetic field maps of the UCNτ Halbach array and ab initio simulations of the loaded ultracold neutron (UCN) phase space distribution into a semiclassical spin-tracking Monte Carlo model developed to account for entanglement between spatial and spin degrees of freedom. This goal will ensure that the characterization of systematic effects associated with spin dynamics (depolarization) keeps pace with anticipated improvements in statistical precision. The second core activity is to develop a real-time monitor for the UCNτ effort that will place run-by-run empirical limits on the depolarization rate and serve as a cross-check of the computational model. The third objective is to develop a quantum sensor, based on Nitrogen-Vacancy defects in diamond, optimized to aid in the control and characterization of magnetic and electric fields for nEDM experiments, thereby enhancing the sensitivity with which the neutron electric dipole moment can be measured.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.