Precision Studies in Subatomic Systems

亚原子系统的精度研究

• 批准号: 2209484
• 负责人: Dinko Pocanic
• 金额: $ 90万
• 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: 2022
• 资助国家: 美国
• 起止时间: 2022-08-01 至 2025-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2209484&HistoricalAwards=false
• 关键词: Precision; Studies; Subatomic; Systems

This award supports a program of experimental research by the University of Virginia group to explore the limits of our knowledge of certain subatomic particles and of their interactions at the smallest length scale. The project investigates three systems: the pi meson, the muon (a more massive "cousin" of the electron), and the neutron. The research program is focused on the intrinsic low-energy properties of each of them, properties that are sensitive to some of the basic components of the Standard Model (SM). The SM describes all known (to date) elementary particles and their basic characteristics. Determining these properties precisely enough to establish whether they differ from SM predictions has the potential to uncover new physical processes and particles. The project aims to advance basic science in nuclear and elementary particle physics, contribute to building the nation's STEM talent by educating members of the new generation of the STEM workforce, by focusing on its diversity, and tapping the broadest available talent pool. Finally, the project aims to develop new tools in fundamental research with possible broader applications.The proposed research continues an ongoing program of study of the electroweak and strong interactions at low energies. The immediate goals of the project are: (a) carrying out the measurements of the Nab experiment, a program of precise measurements of the neutron beta decay parameters at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory; (b) taking part in the new precise measurement and data analysis of the muon gyromagnetic ratio, the Muon g-2 experiment at Fermilab, and (c) conclusion of the data analysis for the PEN experiment, a precise measurement of the electronic and radiative electronic rare decays of the pion. Nab is a high-rate unpolarized measurement of the electron-antineutrino correlation parameter "a" with accuracy of a few parts in 1000, and a precise measurement of the neutron decay parameter "b", the Fierz interference term. Nab aims to resolve the persistent inconsistencies in the determination of the nucleon axial vector form factor and, consequently, of the Vud term in the Cabibbo-Kobayashi-Maskawa quark mixing matrix. This will ultimately provide new limits on possible extensions of the Standard Model, such as left-right symmetric models, leptoquarks, etc., by exploiting the unique advantages of neutron decay, one of the most basic and theoretically best understood processes in nuclear physics. The Muon g-2 experiment is focused on the hadronic corrections to the extremely precisely predicted electroweak processes that determine the interaction of charged leptons with the vacuum, a research subject with one of the highest potentials for discovery of beyond-SM physics. The Muon g-2 experiment is projected to complete data taking during the award period, and will build on the widely reported result from Run-1. The goal of PEN is to reach the precision of 5 parts in 10,000 for the branching ratio of the electronic decay of the pion, which provides the most accurate experimental test of lepton universality (LU) available. At present, precision of the pi-e2 decay measurements lags behind the SM theoretical predictions by more than an order of magnitude. A number of physics scenarios outside the SM would lead to LU violation. LU, and lepton properties in general, carry added significance due to developments in neutrino physics.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.

该奖项支持弗吉尼亚大学小组的一项实验研究计划，以探索我们对某些亚原子粒子及其在最小长度尺度上相互作用的知识的局限性。 该项目研究了三个系统：π介子，μ子（电子的更大的“表亲”）和中子。 该研究计划的重点是它们中的每一个的固有低能量特性，这些特性对标准模型（SM）的一些基本组成部分敏感。 SM描述了所有已知的（迄今为止）基本粒子及其基本特性。 足够精确地确定这些性质，以确定它们是否与SM预测不同，有可能发现新的物理过程和粒子。 该项目旨在推进核和基本粒子物理学的基础科学，通过教育新一代STEM劳动力的成员，通过关注其多样性，并利用最广泛的可用人才库，为建设国家的STEM人才做出贡献。 最后，该项目旨在开发具有更广泛应用的基础研究新工具。拟议的研究继续了正在进行的低能电弱和强相互作用研究计划。该项目的近期目标是：（a）进行Nab实验的测量，这是一个在橡树岭国家实验室的Spanitus中子源精确测量中子β衰变参数的方案;（B）参与费米实验室新的μ子旋磁比的精确测量和数据分析，μ子g-2实验，以及（c）PEN实验数据分析的结论，PEN实验是对π介子的电子和辐射电子稀有衰变的精确测量。Na B是电子-反中微子关联参数a的高速率非极化测量，其精度为千分之几，并且是中子衰变参数B的精确测量，Fierz干涉项。Nab的目的是解决在确定核子轴向矢量形状因子以及Cabibbo-Kobayashi-Maskawa夸克混合矩阵中的Vud项时持续存在的不一致性。这最终将为标准模型的可能扩展提供新的限制，例如左右对称模型，leptoquark等，利用中子衰变的独特优势，中子衰变是核物理学中最基本和理论上最好理解的过程之一。Muon g-2实验的重点是对极其精确预测的电弱过程进行强子修正，该过程决定了带电轻子与真空的相互作用，这是发现超SM物理学的最高潜力之一。Muon g-2实验预计将在授予期间完成数据采集，并将建立在广泛报道的Run-1结果的基础上。PEN的目标是使π介子电子衰变的分支比达到万分之五的精度，这为轻子普适性（LU）提供了最准确的实验测试。目前，pi-e2衰变测量的精度落后于SM理论预测超过一个数量级。SM之外的许多物理场景将导致LU违规。由于中微子物理学的发展，LU和轻子的性质具有额外的意义。该奖项反映了NSF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

Measurement of the parity-odd angular distribution of γ rays from polarized neutron capture on Cl35

Cl35 极化中子俘获γ射线奇偶角分布的测量

• DOI: 10.1103/physrevc.106.015504
• 发表时间: 2022
• 期刊: Physical Review C
• 影响因子: 3.1
• 作者: Fomin, N.;Alarcon, R.;Alonzi, L.;Askanazi, E.;Baeßler, S.;Balascuta, S.;Barrón-Palos, L.;Barzilov, A.;Blyth, D.;Bowman, J. D.
• 通讯作者: Bowman, J. D.