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

用Nab谱仪精确测量自由中子β衰变中的(V-A)耦合常数比并寻找非标准模型耦合

• 批准号: 1812367
• 负责人: Stefan Baessler
• 金额: $ 48万
• 依托单位: University of Virginia Main Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1812367&HistoricalAwards=false
• 关键词: Precise; Measurement; Ratio; Coupling; Constants

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.

该奖项支持对描述中子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。实验将使用Nab光谱仪完成，该光谱仪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。该项目还为项目的扩展做好了准备，其中可以确定另外两个参数A和B。对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。这个实验项目的目标是测试粒子和相互作用的标准模型，在以前无法进入的区域，或者不那么精确。超越标准模型的物理学发现将对核物理和粒子物理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，这些学生将为他们未来的职业生涯学习宝贵的技能和经验。更具体地说，Nab实验的实验程序的动机是：(1)以前所未有的精度确定自由中子β衰变中耦合常数的比率，lambda =g_V/g_A,(2)有助于测试Cabibbo-Kobayashi-Maskawa （CKM）矩阵的统一性，(3)寻找非标准模型（SM）形式的弱相互作用，表现为标量和/或张量相互作用，即：它们以“错误的”螺旋度与费米子相互作用。目前的《核科学长期计划》专门用一段话来说明这一努力。这些研究是由Nab合作进行的，其中PI是实验经理和DOE项目经理。该奖项支持PI及其团队的具体贡献，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负责开发目前Nab的主要分析方法。此外，PI还将对未来项目进行规划，即对“A”和“B”系数的不确定性进行分析，并对一种新型超镜偏振器概念进行初步设计和原型测试，以最大限度地减少这些测量中的主要系统不确定性。这个项目将对高等教育产生重大影响。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。PI坚决致力于吸引代表性不足群体的成员，以帮助扩大该领域的人力资源基础。物理系成为APS桥梁项目的新基地，而PI是未来的导师。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

The Nab experiment: A precision measurement of unpolarized neutron beta decay

Nab 实验：非极化中子 β 衰变的精确测量

• DOI: 10.1051/epjconf/201921904002
• 发表时间: 2019
• 期刊: EPJ Web of Conferences
• 作者: Fry, J.;Alarcon, R.;Baeßler, S.;Balascuta, S.;Palos, L. Barrón;Bailey, T.;Bass, K.;Birge, N.;Blose, A.;Borissenko, D.
• 通讯作者: Borissenko, D.

Beam dynamics corrections to the Run-1 measurement of the muon anomalous magnetic moment at Fermilab

• DOI: 10.1103/physrevaccelbeams.24.044002
• 发表时间: 2021-04-27
• 期刊: PHYSICAL REVIEW ACCELERATORS AND BEAMS
• 影响因子: 1.7
• 作者: Albahri, T.;Anastasi, A.;Wu, W.
• 通讯作者: Wu, W.

Using Nab to determine correlations in unpolarized neutron decay

使用 Nab 确定非极化中子衰变的相关性

• DOI: 10.1007/s10751-018-1538-7
• 发表时间: 2019
• 期刊: Hyperfine Interactions
• 作者: Broussard, L. J.;Baeßler, S.;Bailey, T. L.;Birge, N.;Bowman, J. D.;Crawford, C. B.;Cude-Woods, C.;Fellers, D. E.;Fomin, N.;Frlež, E.
• 通讯作者: Frlež, E.

Improved determination of the β−ν¯e angular correlation coefficient a in free neutron decay with the aSPECT spectrometer

使用 aSPECT 能谱仪改进自由中子衰变中 β-δe 角相关系数 a 的测定

• DOI: 10.1103/physrevc.101.055506
• 发表时间: 2020
• 期刊: Physical Review C
• 影响因子: 3.1
• 作者: Beck, M.;Ayala Guardia, F.;Borg, M.;Kahlenberg, J.;Muñoz Horta, R.;Schmidt, C.;Wunderle, A.;Heil, W.;Maisonobe, R.;Simson, M.
• 通讯作者: Simson, M.

Design and test of a compact and high-resolution time-of-flight measurement device for cold neutron beams

紧凑型高分辨率冷中子束飞行时间测量装置的设计与测试

• DOI: 10.1103/physrevaccelbeams.22.032801
• 发表时间: 2019
• 期刊: Physical Review Accelerators and Beams
• 影响因子: 1.7
• 作者: Roulier, Damien;Nesvizhevsky, Valery;Clément, Benoît;Freche, Guilhem;Pignol, Guillaume;Rebreyend, Dominique;Vezzu, Francis;Baeßler, Stefan;Strelkov, Alexander
• 通讯作者: Strelkov, Alexander