Fundamental Physics with Cold Polarized Neutrons

冷极化中子的基础物理

• 批准号: 0855694
• 负责人: Timothy Chupp
• 金额: $ 54万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0855694&HistoricalAwards=false
• 关键词: Fundamental; Physics; Cold; Polarized; Neutrons

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.

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内，中子保持稳定，但当脱离原子核时，它是不稳定的。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组分和衰变产物之间的相互作用。 中子也有自旋，这是最基本的物质的量子力学性质，它区分了两种状态，称为自旋向上和自旋向下。自旋是核磁共振和核磁共振成像中所利用的核磁的原因。自旋态也影响中子的衰变和相互作用，因此控制中子自旋对于更详细地研究亚原子相互作用变得有用。该奖项资助了一项计划，以深入细致地推进中子寿命的精度和准确度，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，朝着一种新的冷中子束测量中子寿命的方向发展：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，将测量质子不对称性，并使用精确极化冷中子束来寻找标量流和其他新物理。需要非常精确地测量中子极化（即所选自旋状态的过量部分）和精确的自旋反转，以减轻这些实验中可能出现的假效应。He-3极化、自旋过滤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层智力问题。其目的是收集数据，这将有助于完成基本粒子及其相互作用的图片。这些技术具有更广泛的影响。在相关实验中使用的激光偏振He-3和He-129现在用于生物医学研究，材料科学和量子信息研究。该项目是本科生和研究生的一个显着的培训基地。技术挑战与深刻的知识问题相结合，提供动力并发展技术技能。本科生将获得研究经验的工作沿着与研究生和博士后研究员。研究生出现广泛的能力，并继续为教师或国家实验室职位以及跨学科研究做准备。这项工作还导致了非物理专业的新课程的开发，一套关于核磁体和中微子的公开讲座，以及向感兴趣的公众传播科学的领导地位。在探索物理学基本问题的背景下，最困难的问题产生了最具创新性的解决方案，其副产品在一开始是不可想象的。原子钟、增强型核磁共振成像和探测物质起源的实验都是由核磁和中子自旋控制的。