Precision Experiments with Cold and Ultracold Neutrons

冷和超冷中子的精密实验

• 批准号: 1506320
• 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: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1506320&HistoricalAwards=false
• 关键词: Precision; Experiments; Cold; Ultracold; Neutrons

Research in Fundamental Nuclear and Particle Physics is being categorized in three areas: At the "Energy Frontier", physicists hope to discover new physics, e.g. new symmetries or particles, by colliding particles with increasingly high energy. At the "Cosmic Frontier", physicists use the cosmos as a laboratory that contains detectable information about new physics. And finally, at the "Precision Frontier", physicists attempt to measure quantities that are believed to be known very precisely, and to interpret deviations from the known physics predictions as a signal for new physics. This award supports a measurement of the third type, a precision measurement of several observables in free neutron beta decay which serve to better understand the fundamental interactions between elementary particles. The process of beta decay has been incorporated into the standard model of elementary particle physics, which gives us a successful description of elementary particle processes. A discovery of new physics would have a critical impact on Nuclear and High Energy Physics, and on Cosmology. Being on the forefront of scientific research and on the edge of what is technologically feasible, the project will serve as a training ground for future generations of scientists. Most of the research will be done by students at the undergraduate and graduate level. This grant supports the effort to design, construct, commission, and operate the Nab spectrometer. The spectrometer will use the state of the art neutron beamline (FNPB) at the new Spallation Neutron Source (SNS) in Oak Ridge, TN to determine the two-dimensional energy distribution of decay electron and protons in neutron beta decay. The redundancy inherent in the standard model description of the neutron beta decay process allows uniquely sensitive checks of the model's validity and limits, with strong implications in astrophysics. One of the expected observables, the determination of the neutrino-electron-correlation coefficient with a relative uncertainty of 0.1%, will allow an extraction of Vud, the upper left element of the Cabbibo-Kobayashi-Maskawa (CKM) matrix, in order to test its unitarity. The current NSAC long range plan finds that "The only realistic way to improve Vud is via neutron decay." New results from high energy physics cast a shadow on the unitarity of the CKM matrix, and re-open the possibility of finding hints for new exchange bosons, or a fourth quark generation. The other observable, the determination of the Fierz term, which parametrizes a deviation from the known shape of the spectrum of the decay electrons, to about 0.001, allows finding new particles that mediate scalar or tensor interactions at low energy, in a complementary way and with sensitivity competitive to what is expected from LHC.

基本核和粒子物理学的研究正在分为三个领域：在“能量边界”，物理学家希望发现新物理学，例如新的对称性或颗粒，通过具有越来越高的能量的粒子碰撞。在“宇宙边界”中，物理学家使用宇宙作为一个实验室，其中包含有关新物理学的可检测信息。最后，在“精确边界”上，物理学家试图测量被认为是非常精确的数量，并将与已知物理学预测的偏差解释为新物理学的信号。该奖项支持对第三种类型的测量，这是对自由中子β衰变中几个可观察力的精确度量，这些测量可更好地了解基本颗粒之间的基本相互作用。 β衰变的过程已纳入基本粒子物理的标准模型中，这使我们成功地描述了基本粒子过程。新物理学的发现将对核和高能量物理学以及宇宙学产生关键影响。 在科学研究的最前沿，在技术上可行的边缘，该项目将成为子孙后代科学家的训练场。大多数研究将由学生和研究生层面的学生完成。该赠款支持设计，构建，委托和操作NAB光谱仪的努力。光谱仪将在田纳西州Oak Ridge的新散布中子源（SNS）处使用最先进的中子光束线（FNPB）的状态，以确定中子β衰变中衰减电子和质子的二维能量分布。中子β衰变过程的标准模型描述中固有的冗余性允许对模型的有效性和限制进行独特的敏感检查，并在天体物理学中具有很大的影响。 一个预期的可观察到的是，确定中微子 - 电子相关系数，相对不确定性为0.1％，将允许提取VUD，VUD是Cabbibo-Kobayashi-Maskawa（CKM）基质的左上元素，以测试其单位性。 当前的NSAC远程计划发现“改善VUD的唯一现实方法是通过中子衰减。”高能量物理学的新结果对CKM矩阵的单位性产生了阴影，并重新打开了寻找新的交换玻色子或第四夸克一代的提示的可能性。另一个可观察的是，fierz项的确定是从已知的衰减电子光谱形状的偏差到约0.001的偏差，允许找到以互补的方式和低能量介导的标量或张量相互作用的新粒子，并且具有LHC的敏感性竞争性。

项目成果

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.