Fundamental Physics with Cold Polarized Neutrons

中子是一种亚原子粒子，占世界物质的一半以上。在大多数原子的原子核中，中子保持稳定，但当它从原子核中释放出来时，它就不稳定了。自由中子是研究亚原子物理的重要工具，因为自由中子的衰变和相互作用揭示了其成分和衰变产物的相互作用。中子也有自旋，这是物质最基本的量子力学特性，区分了自旋向上和自旋向下两种状态。自旋是核磁被利用的原因，例如，在核磁共振和核磁共振中。自旋态也影响中子的衰变和相互作用，因此对中子自旋的控制对亚原子相互作用的更详细的研究是有用的。该奖项资助了一个项目，旨在深入细致地推进中子寿命的精度和准确性，辐射衰变分支的测量和中子衰变相关系数的测量。三个相互交织的项目正在进行中：1)通过从中子束通量的量热测量转移校准，向新的冷中子束测量中子寿命的进展；2)在扩展的光子能量范围内精确测量中子衰变中的辐射衰变分支；3)发展实验原理和仪器，用精密极化冷中子束测量质子不对称性，寻找标量电流和其他新的物理现象。需要非常精确地测量中子极化（即所选自旋态的多余部分）和精确的自旋反转，以减轻这些实验中可能出现的错误效应。He-3极化、自旋滤波和自旋翻转技术将得到很大的改进。这部作品探讨了关于物质最基本部分的深刻的智力问题。目的是收集数据，以帮助完成基本粒子及其相互作用的图景。这些技术有更广泛的影响。用于相关实验的激光偏振光He-3和Xe-129现已应用于生物医学研究、材料科学和量子信息研究。这个项目对本科生和研究生来说是一个很好的训练基地。技术挑战与深刻的智力问题相结合，提供了动力和发展技术技能。本科生将获得与研究生和博士后一起工作的研究经验。研究生具备广泛的能力，并继续为教师或国家实验室职位以及跨学科研究做准备。这项工作也导致了非物理专业新课程的发展，一系列关于核磁体和中微子的公开讲座，以及向感兴趣的普通大众传播科学的领导作用。在探索物理学基本问题的背景下，最难的问题本身就令人兴奋，产生了最具创新性的解决方案，并带来了最初难以想象的副产品。原子钟，增强的核磁共振成像，以及探测物质起源的实验，都源于对核磁和中子自旋的控制。

The neutron is a subatomic particle that comprises more than half of the matter in the world. Within the nuclei of most atoms, the neutron remains stable, but when freed from the nucleus, it is unstable. Free neutrons are an important tool for study of subatomic physics, because the decay and interactions of free neutrons reveal the interactions of its constituents and decay products. Neutrons also have spin, the quantum mechanical property of the most fundamental pieces of matter that distinguishes two states called spin-up and spin-down. Spin is responsible for the nuclear magnetism exploited, for example, in NMR and MRI. The spin states also affect the decay and interactions of neutrons, and so the control of neutron spin becomes useful for more detailed study of subatomic interactions. This award funds a program to incisively and carefully advance both the precision and the accuracy of the neutron lifetime, measurement of the radiative decay branch and measurement of correlation coeffcients in neutron decay. Three intertwined projects are underway: 1) advances toward a new cold-neutron beam measurement of the neutron lifetime by transfer of calibration from a calorimetric measurement of the neutron beam flux; 2) precision measurement of the radiative decay branch in neutron decay over an extended range of photon energies; 3) development of experimental principles and apparatus that will measure the proton asymmetry and search for Scalar currents and other new physics with a precision polarized cold neutron beam. Very precise measurement of the neutron polarization (i.e. the excess fraction of the selected spin state) and precise spin reversal are required to mitigate false effects that may arise in these experiments. The techniques of He-3 polarization, the spin filter and spin flipping will be greatly improved. This work probes deep intellectual questions about the most fundamental pieces of matter. The aim is to collect data that will help complete the picture of elementary particles and their interactions. The techniques have much broader impact. Laser polarized He-3 and Xe-129 used in related experiments are now used in biomedical research, materials science, and quantum information research.This project is a remarkable training ground for undergraduate and graduate students. The technical challenges combined with the deep intellectual issues provide motivation and develop technical skills. Undergraduates will gain research experience working along with graduate and post doctoral fellows. Graduate students emerge broadly capable and move on to prepare for faculty or national lab positions as well as interdisciplinary research. This work has also led to development of new courses for nonphysics majors, to a set of public lectures on Nuclear Magnets and Neutrinos and leadership in communicating science to the interested general population. In the context of probing fundamental problems of physics, exciting in its own right, the hardest problems produce the most innovative solutions with spin-offs unimaginable at the outset. Atomic clocks, enhanced MRI, and experiments that probe the origin of matter all follow from the control of nuclear magnetism and neutron spins.