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 and pNab Spectrometers

使用 Nab 和 pNab 谱仪精确测量自由中子 Beta 衰变中的 (V-A) 耦合常数比并搜索非标准模型耦合

• 批准号: 2111363
• 负责人: Stefan Baessler
• 金额: $ 48.5万
• 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: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2111363&HistoricalAwards=false
• 关键词: Precise; Measurement; Ratio; Coupling; Constants

This grant supports the measurement of angular correlation coefficients describing neutron beta decay using the “Nab” spectrometer at Oak Ridge National Laboratory. In this experiment the "a" and "b" coefficients describe the proton and electron resulting from the decay of the neutron. The main purpose of the measurements is to test the Standard Model of Nuclear and Particle Physics, which has been extremely successful in describing most of the properties and behavior of the elementary particles to date but leaves open critical questions such as the reason for the dominance of matter over anti-matter in the universe. A discovery of Beyond the Standard Model physics would thus have important implications for Physics and Cosmology. Installation of the Nab spectrometer at the Spallation Neutron Source (SNS) at Oak Ridge will be finished by the end of summer 2021, and commissioning and data taking will commence and continue for the duration of the proposal period. The PI is the project manager for the Nab collaboration. This grant will fund the PI’s group, and they will participate in data taking, detector simulation, data analysis, and characterization of the proton detection efficiency. The PI is strongly committed to attracting members of underrepresented groups. The University of Virginia physics department recently became a new site for the APS bridge program, and the PI is serving as a mentor. Furthermore, the project has a valuable impact on higher education: most of the work is done by students at undergraduate and graduate level, and these students will earn valuable skills and experiences for their future careers.The redundancy inherent in the Standard Model description of the neutron beta decay process allows for sensitive checks of the model’s validity. One of the expected observables (the neutrino-electron-correlation coefficient “a”) will allow an extraction of 𝑉𝑢𝑑, the upper left element of the Cabbibo-Kobayashi-Maskawa (CKM) matrix, in order to test the unitarity of the matrix. A recent re-evaluation of the world’s data suggests that CKM matrix unitarity is violated and so the results of the Nab experiment are eagerly anticipated. The other observable (The Fierz term “b”) allows us to test for scalar or tensor interactions at low energies, in a complementary way, and with sensitivity competitive to what is expected from the LHC. The current Long Range Plan for Nuclear Science devotes a paragraph to this effort (see LRP, page 75).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.

这笔赠款支持使用橡树岭国家实验室的“NAB”光谱仪测量描述中子β衰变的角相关系数。在这个实验中，“a”和“b”系数描述了由于中子衰变而产生的质子和电子。测量的主要目的是测试核物理和粒子物理的标准模型，该模型迄今在描述基本粒子的大多数性质和行为方面非常成功，但留下了一些关键问题，如宇宙中物质凌驾于反物质之上的原因。因此，超越标准模型物理学的发现将对物理学和宇宙学产生重要影响。橡树岭散裂中子源的NAB光谱仪安装工作将于2021年夏季结束前完成，调试和数据采集将在提议期间开始并继续进行。PI是NAB协作的项目经理。这笔赠款将资助PI的小组，他们将参与数据采集、探测器模拟、数据分析和质子探测效率的表征。国际和平协会坚决致力于吸引代表人数不足的群体的成员。弗吉尼亚大学物理系最近成为APS桥项目的新地点，PI担任导师。此外，该项目对高等教育产生了宝贵的影响：大部分工作是由本科生和研究生完成的，这些学生将为他们未来的职业生涯获得宝贵的技能和经验。标准模型对中子β衰变过程的描述中固有的冗余允许对模型的有效性进行敏感的检查。其中一个预期观测(中微子-电子相关系数“a”)将允许提取卡比博-小林-马斯卡瓦(CKM)矩阵的左上角元素𝑉𝑢𝑑，以测试该矩阵的统一性。最近对世界数据的重新评估表明，CKM矩阵的单位性被破坏，因此NAB实验的结果是令人热切期待的。另一个可观测的(菲尔兹项“b”)使我们能够测试低能下的标量或张量相互作用，以一种互补的方式，并以与大型强子对撞机预期的灵敏度竞争的方式。当前的核科学长期计划中有一段是关于这一努力的(见LRP，第75页)。这一奖项反映了NSF的法定使命，并通过使用基金会的学术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

Precision pulse shape simulation for proton detection at the Nab experiment

Nab 实验中质子检测的精确脉冲形状模拟

• DOI: 10.1103/physrevc.107.065503
• 发表时间: 2023
• 期刊: Physical Review C
• 影响因子: 3.1
• 作者: Hayen, Leendert;Choi, Jin Ha;Combs, Dustin;Taylor, R. J.;Baeßler, Stefan;Birge, Noah;Broussard, Leah J.;Crawford, Christopher B.;Fomin, Nadia;Gericke, Michael
• 通讯作者: Gericke, Michael

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.