High Precision Measurements of Beta Decay Using Stored Ultracold Neutrons and Cold Neutron Beams

使用储存超冷中子和冷中子束高精度测量β衰变

• 批准号: 1914133
• 负责人: Albert Young
• 金额: $ 66.5万
• 依托单位: North Carolina State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-07-15 至 2023-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1914133&HistoricalAwards=false
• 关键词: Precision; Measurements; Beta; Decay; Using

This award supports high precision measurements of neutron beta decay, a process in which a neutron decays, because of the weak nuclear force (or weak interaction), into a proton, an electron and an anti-neutrino. The weak nuclear force is important, in that it powers our sun and helps determine the abundance of elements in the universe. Neutron decay is also important because it involves only a single nucleon, making possible very precise predictions from the "standard model" of particle physics without the complications due to the presence of other nucleons. With very accurate measurements of neutron decay, we can perform a kind of particle physics "forensics", looking for discrepancies in our standard model which can indicate the presence of new forces, but without using high energy particle beams such as those at the Large Hadron Collider at CERN. This research is a part of the "precision frontier" for physics, and defines the cutting edge of our knowledge of the weak nuclear force and possible new interactions. The PI and his group contribute to a new measurement of the neutron's lifetime (UCNtau) and an angular correlation measurement (Nab). The lifetime and angular correlations measurements probe different aspects of the weak interaction, and if successful, will sharpen our knowledge of critical components of the weak interaction and contribute to strong limits on extensions the standard model, at or above those which are being established at CERN. An important aspect of the project is the training of students and post-docs. This training comes in part because of the specific nature of the research projects, which utilize nuclear physics analysis and technology (which also has real-world applications in energy generation and medical imaging, for example) and in part from the many opportunities students working in the program have to perform research at national laboratories and nuclear facilities. One of the experiments supported by the award, Nab, will use an unpolarized beam of cold neutrons at the Spallation Neutron Source from the Oak Ridge National Laboratory to measure the angular correlation between the decay electron and the anti-neutrino (called the electron-anti-neutrino correlation), with the goal of over an order of magnitude improvement in the precision of this parameter. The other, UCNtau, is situated at the ultracold neutron (UCN) source at Los Alamos National Laboratory (LANL), and targets precision levels below 0.3 seconds during the current funding period. The impact of these programs being successful are: (1) knowledge of the axial form factor at the level required to determine the CKM matrix element Vud at the same level as the current theoretical uncertainty for the electro-weak radiative corrections, (2) knowledge of the lifetime at a level such that it will limit tests of our models for the cosmological He-4 abundance for some time, and (3) limits on tensor couplings at or above the level expected from CERN. Motivation for these measurements has been amplified over the last year by theoretical progress on the electroweak radiative corrections and lattice calculations of the axial coupling constant, with both opening new, higher precision probes for new physics. For each of these experiments, this group brings its experience in beta decay measurements to bear on key sources of systematic error by developing instrumentation and analysis required by the experiments. For Nab, for example, the group is analyzing the effects of incomplete collection of the energy of decay electrons and the calibration procedures, a critical component of the systematic error budget for this experiment. UCNtau is designed to store UCNs in a magneto-gravitational trap, where the UCNs do not contact with the trap walls. The top of the trap is open, permitting detectors to be lowered into the trap to measure UCN populations and determine the lifetime. The group will continue to develop UCN detectors for this purpose and focus additional effort on understanding systematic errors due to UCNs with high enough energies to slowly escape the trap and shift the measured value of the lifetime. These tasks are essential and ongoing parts of the planned experiments, with completed measurements and analysis incorporated into publications during the proposal period.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.

该奖项支持中子β衰变的高精度测量，这是一个中子衰变的过程，由于弱核力（或弱相互作用），成为质子，电子和反中微子。 弱核力很重要，因为它为我们的太阳提供动力，并帮助确定宇宙中元素的丰度。 中子衰变也很重要，因为它只涉及单个核子，使得粒子物理学的“标准模型”可以非常精确地预测，而不会因为其他核子的存在而变得复杂。 通过非常精确的中子衰变测量，我们可以进行一种粒子物理学“取证”，寻找我们的标准模型中的差异，这可以表明新的力量的存在，但不使用高能粒子束，如欧洲核子研究中心的大型强子对撞机。 这项研究是物理学“精确前沿”的一部分，并定义了我们对弱核力和可能的新相互作用的知识的前沿。 PI和他的团队为中子寿命（UCNtau）和角相关测量（Nab）的新测量做出了贡献。 寿命和角度相关测量探测弱相互作用的不同方面，如果成功的话，将提高我们对弱相互作用关键组成部分的认识，并有助于对标准模型的扩展进行严格限制，达到或超过CERN正在建立的标准模型。 该项目的一个重要方面是学生和博士后的培训。这种培训部分是因为研究项目的具体性质，这些项目利用核物理分析和技术（例如，在能源生产和医学成像方面也有实际应用），部分是因为在该计划中工作的学生有许多机会在国家实验室和核设施进行研究。 该奖项支持的实验之一Nab将在橡树岭国家实验室的Spectron中子源上使用非偏振冷中子束来测量衰变电子和反中微子之间的角相关（称为电子-反中微子相关），目标是将该参数的精度提高一个数量级以上。 另一个是UCNTau，位于洛斯阿拉莫斯国家实验室（LANL）的超冷中子（UCN）源，目标是在当前资助期间达到0.3秒以下的精度水平。这些方案取得成功的影响是：（1）在与电弱辐射校正的当前理论不确定性相同的水平上确定CKM矩阵元Vud所需的水平上的轴向形状因子的知识，（2）在一定水平上的寿命的知识，使得它将在一段时间内限制我们的宇宙学He-4丰度模型的测试，和（3）张量耦合的限制在或高于CERN预期的水平。 在过去的一年里，这些测量的动机被电弱辐射校正和轴向耦合常数的晶格计算的理论进展所放大，这两个方面都为新物理学开辟了新的，更高精度的探针。对于这些实验中的每一个，该小组通过开发实验所需的仪器和分析，将其在β衰变测量方面的经验用于系统误差的关键来源。 例如，对于Nab，该小组正在分析衰变电子能量的不完全收集和校准程序的影响，这是该实验系统误差预算的关键组成部分。 UCNTau被设计成将UCN存储在磁引力阱中，其中UCN不与阱壁接触。 陷阱的顶部是开放的，允许探测器下降到陷阱中，以测量UCN的人口和确定的寿命。 该小组将继续为此目的开发UCN探测器，并将更多的精力集中在理解由于具有足够高能量的UCN而导致的系统误差上，以缓慢地逃离陷阱并改变寿命的测量值。 这些任务是计划中的实验的基本和持续的部分，在建议期间完成的测量和分析被纳入出版物。该奖项反映了NSF的法定使命，并被认为是值得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的支持。

项目成果

Monte Carlo simulations of trapped ultracold neutrons in the UCNτ experiment

UCNÏ 实验中捕获的超冷中子的蒙特卡罗模拟

• DOI: 10.1103/physrevc.100.015501
• 发表时间: 2019
• 期刊: Physical Review C
• 影响因子: 3.1
• 作者: Callahan, Nathan;Liu, Chen-Yu;Gonzalez, Francisco;Adamek, E.;Bowman, J. D.;Broussard, L.;Clayton, S. M.;Currie, S.;Cude-Woods, C.;Dees, E. B.
• 通讯作者: Dees, E. B.

Standard model O(α) renormalization of gA and its impact on new physics searches

gA 的标准模型 O(α) 重整化及其对新物理搜索的影响

• DOI: 10.1103/physrevd.103.113001
• 发表时间: 2021
• 期刊: Physical Review D
• 影响因子: 5
• 作者: Hayen, Leendert

New high-sensitivity searches for neutrons converting into antineutrons and/or sterile neutrons at the HIBEAM/NNBAR experiment at the European Spallation Source

• DOI: 10.1088/1361-6471/abf429
• 发表时间: 2020-06
• 期刊: Journal of Physics G: Nuclear and Particle Physics
• 作者: A. Addazi;K. Anderson;S. Ansell;K. Babu;J. Barrow;D. Baxter;P. Bentley;Z. Berezhiani;R. Bevilacqu

Improved limits on Fierz interference using asymmetry measurements from the Ultracold Neutron Asymmetry (UCNA) experiment

使用超冷中子不对称 (UCNA) 实验的不对称测量改进了 Fierz 干扰的限制

• DOI: 10.1103/physrevc.101.035503
• 发表时间: 2020
• 期刊: Physical Review C
• 影响因子: 3.1
• 作者: Sun, X.;Adamek, E.;Allgeier, B.;Bagdasarova, Y.;Berguno, D. B.;Blatnik, M.;Bowles, T. J.;Broussard, L. J.;Brown, M. A.-P.;Carr, R.
• 通讯作者: Carr, R.

Ultracold neutron properties of the Eljen-299-02D deuterated scintillator

Eljen-299-02D 氘化闪烁体的超冷中子特性

• DOI: 10.1063/5.0030972
• 发表时间: 2021
• 期刊: Review of Scientific Instruments
• 影响因子: 1.6
• 作者: Tang, Z.;Watkins, E. B.;Clayton, S. M.;Currie, S. A.;Fellers, D. E.;Hassan, Md. T.;Hooks, D. E.;Ito, T. M.;Lawrence, S. K.;MacDonald, S. W.
• 通讯作者: MacDonald, S. W.