Precise Measurement of the Ratio of (V-A) Coupling Constants in Free Neutron Beta Decay and Search for Non-Standard Model Couplings with the Nab spectrometer

该奖项支持对描述中子如何衰变的两个关键参数的测量。这些参数被称为“小a”和“小b”，它们与衰变产物的动量和放射性衰变的强度有关。这项实验将使用目前安装在橡树岭国家实验室散裂中子源的基本中子物理光束线上的NAB能谱仪进行。该项目还为程序的扩展铺平了道路，可以确定另外两个参数A和B。这些参数的精确测量有助于更好地理解基本粒子之间的基本相互作用。这个实验计划的目标是测试粒子和相互作用的标准模型，这些粒子和相互作用在以前无法进入或不那么精确的区域。超越标准模型的物理学的发现将对核物理和粒子物理学以及宇宙学产生重要影响。该项目将对高等教育产生宝贵的影响：大部分工作将由本科生和研究生完成，这些学生将为未来的职业生涯学到宝贵的技能和经验。更具体地说，NAB实验的实验方案的动机是(1)以前所未有的精度确定自由中子β衰变中的耦合常数的比率，lambda=g_V/g_A，(2)有助于测试Cabibbo-Kobayashi-Maskawa(CKM)矩阵的唯一性，以及(3)寻找表现为标量和/或张量相互作用的非标准模型(SM)形式的弱相互作用，即与具有“错误的”螺旋度的费米子相互作用。目前的核科学远程计划中有一段专门介绍了这方面的工作。研究由NAB协作组进行，其中PI是实验经理，DOE项目经理。该奖项支持PI和他的团队的具体贡献，其中最重要的是超导磁体的表征，光谱仪真空系统、高压和主电极的组装和表征，以及专用质子源中质子探测效率的表征。PI负责发展目前NAB的主要分析方法。此外，PI将致力于未来计划的规划，即分析“A”和“B”系数的不确定度，以及初步设计和原型测试一种新的超级反射镜偏振器概念，以将这些测量中的领先系统不确定度降至最低。该项目将对高等教育产生宝贵的影响。几名本科生和研究生将在拟议的项目中获得宝贵的研究经验。国际和平协会坚定地致力于吸引任职人数不足的群体成员，以帮助扩大外地的人力资源基础。物理系成为APS桥梁项目的新地点，PI是未来的导师。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award supports the measurement of two key parameters that describe how a neutron decays. Those parameters are called "little a" and "little b", and they are related to the momentum of the decay products and to the strength of the radioactive decay. The experiment will be done with the Nab spectrometer that is presently being installed at the Fundamental Neutron Physics Beamline at the Spallation Neutron Source at the Oak Ridge National Laboratory. This project also prepares the way for an extension of the program, in which two more parameters, A and B, can be determined. The precise measurement of these parameters furthers a better understanding of the fundamental interactions between elementary particles. The goal of this experimental program is to test the Standard Model of particles and interactions in regions that were inaccessible before, or not as precise. A discovery of physics beyond the Standard Model would have important implications for nuclear and particle physics, as well as cosmology. The project will have a valuable impact on higher education: most of the work will be done by students at undergraduate and graduate levels, and these students will learn valuable skills and experiences for their future careers. More specifically, the motivation for the experimental program for the Nab experiment is to (1) determine the ratio of the coupling constants in free neutron beta decay, lambda =g_V/g_A, with unprecedented precision, (2) to contribute to a test of the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix, and (3) to search for non-Standard Model (SM) forms of weak interaction that manifest themselves as scalar and/or tensor interactions, that is, which interact with fermions with the "wrong" helicity. The current Long Range Plan for Nuclear Science devotes a paragraph to this effort. The studies are performed by the Nab collaboration, of which the PI is the experiment manager and the DOE project manager. The award supports the specific contributions of the PI and his group, the most important of which are the characterization of the superconducting magnet, the assembly and characterization of the spectrometer vacuum system, high voltage and main electrodes, and the characterization of the efficiency of the proton detection in a dedicated proton source. The PI is responsible for the development of the present main analysis method for Nab. In addition, the PI will work on the planning of the future program, which is the analysis of uncertainties for the "A" and "B" coefficients, and the preliminary design and prototype testing of a novel supermirror polarizer concept that would minimize the leading systematic uncertainty in those measurements. The project will have a valuable impact on higher education. Several undergraduate and graduate students will gain valuable research experience working on the proposed projects. The PI is strongly committed to attracting members of underrepresented groups, to help broaden the human resource base of the field. The physics department became a new site for the APS bridge program, and the PI is a prospective mentor.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.