RUI: Precision Weak Interaction Studies in Nuclei

该奖项支持的研究将探索我们对弱相互作用的理解极限，弱相互作用是自然的四种基本力量之一。在其他方面，弱相互作用导致了一种称为贝塔衰变的放射性衰变，在这种衰变中，一个原子核随着一个电子和一个中微子的发射而转变为另一个不同的原子核。该奖项将允许这两位科学家进行实验，在这些实验中，他们可以精确地测量在四种不同的核β衰变中发射的电子的能量。其中三个实验将测试电弱相互作用标准模型的关键方面，该模型是描述两种基本力--弱相互作用和电磁相互作用--统一的理论。这些精确的β衰变测量是粒子对撞机实验在寻找新物理方面的补充。第四个拟议的实验旨在解决钾-40贝塔衰变的不确定性，钾-40是地质年代学的重要工具。该研究计划的进一步目标和效益是培养高素质的本科物理人才。参与的学生将获得最先进的软件和实验技术的经验，并将学习独立思考和获得各种实用的解决问题的技能。当这些学生进入STEM领域或从事教学工作时，就会感受到更广泛的影响。该研究计划包括几个实验，涉及高精度测量β光谱的形状。在两个拟议的实验中，目标是在粒子物理标准模型的电弱部分对守恒矢量电流假说进行强有力的测试。在第三个实验中，目标是改进对描述弱相互作用的非标准模型贡献(Fierz项)的限制。第四个实验的目标是解决与地质年代学应用相关的钾-40贝塔光谱中的不确定性。具体地说，将使用威斯康星大学麦迪逊分校的一种新的磁谱仪来测量碳14β光谱。该光谱仪将与用于在氧-14中进行相同测量的超导光谱仪在形式上几乎相同，从而能够减少由高阶矩阵元素贡献引起的不确定度。氟-20和氦-6的测量将在国家超导回旋加速器实验室进行，使用植入闪烁体探测器，这将具有与磁谱仪测量显著不同的系统效应，对于实现低阈值将是重要的。第四个实验的目标是测量钾-40贝塔光谱的形状。了解这种光谱形状对于地质样品放射性测年的标准技术很重要，但最近的一份报告表明，这种形状可能没有人们想象的那么好。所有这些测量的一个重要方面是通过测量和计算建模来评估和校正系统效应。

The research supported by this award will probe the limits of our understanding of the weak interaction, one of the four fundamental forces of nature. Among other things, the weak interaction is responsible for the type of radioactive decay called beta decay in which a nucleus is transformed into a different nucleus with the emission of an electron and a neutrino. The award will allow the two scientists to carry out experiments in which they precisely measure the energy of electrons emitted in four different nuclear beta decays. Three of these experiments will test key aspects of the Standard Model of the electroweak interaction, which is the theory that describes the unification of two of the fundamental forces, the weak interaction and the electromagnetic interaction. These precision beta decay measurements are complementary to particle collider experiments in the search for new physics. A fourth proposed experiment aims to resolve uncertainties in the beta decay of potassium-40, an important tool in geochronology. The research program has the further goal and benefit of training highly talented undergraduate physics students. Students involved will gain experience with state-of-the-art software and experimental techniques, and will learn to think independently and gain a variety of practical problem solving skills. The broader impact is felt when these students enter the workforce in STEM fields or in teaching. The research program consists of several experiments involving the high precision measurement of the shapes of beta spectra. In two of the proposed experiments the goal is to provide a strong test of the Conserved Vector Current hypothesis in the electroweak sector of the Standard Model of particle physics. In a third experiment, the goal is to improve limits on non-Standard-Model contributions (Fierz terms) to the description of the weak interaction. A fourth experiment has the goal of resolving an uncertainty in the potassium-40 beta spectrum, which is relevant to applications in geochronology. Specifically, the carbon-14 beta spectrum will be measured using a new magnetic spectrometer at the University of Wisconsin-Madison. This spectrometer will be nearly identical in form to the superconducting spectrometer used to make the same measurement in oxygen-14, enabling reduced uncertainties arising from higher order matrix element contributions. Measurements in fluorine-20 and helium-6 will be carried out at the National Superconducting Cyclotron Laboratory using implantation into a scintillator detector, which will have significantly different systematic effects from the magnetic spectrometer measurements and will be important in achieving low thresholds. A fourth experiment has the goal of measuring the shape of the potassium-40 beta spectrum. Knowledge of this spectrum shape is important for a standard technique in radioactive dating of geologic samples, but a recent report suggests the shape may not be as well understood as had been thought. An important aspect of all these measurements is in assessing and correcting for systematic effects through measurement and computational modeling.