Collaborative Research: PM: High-Z Highly Charged Ions Probing Nuclear Charge Radii, QED, and the Standard Model

该项目由原子、分子和光学实验物理、刺激竞争性研究的既定计划（EPSCoR）和实验核物理共同资助。当原子外层的许多电子被移走时，它就变成了一个高电荷离子。这种高电荷离子（HCI）很有趣，因为与中性原子相比，它们具有奇异的性质。在这些离子中，剩余的电子是那些与小的中心核明显重叠的电子。对电子改变轨道时发出的光进行精确测量，从而获得有关原子核的信息。这些包括有限核电荷半径、核变形和磁性。利用电子束离子阱（EBIT），该项目旨在对选择具有简单的、理论上可计算的电子构型的HCI进行实验研究，以了解核效应。通过测量极紫外（EUV）和x射线区域的辐射，pi和他们的合作者最近使用na和mg类离子进行了一系列基准实验，并确定了高z同位素的核电荷半径差异。在目前的项目中，他们将扩展这些研究，调查其局限性，并探索其对超越标准模型（BSM）物理的敏感性。该研究还将用于改进现有的复杂原子系统的原子理论。研究生和本科生将参与实验设置、数据收集、分析、解释、科学报告撰写和会议报告。这项研究工作将与学生们所参加的跨学科教育项目相结合，如克莱姆森大学的“创造性探究”项目和阿巴拉契亚州立大学的“实验物理方法”。来自弱势群体的学生将被鼓励参与研究工作，研究生将被训练来指导本科生。只有少数几种方法可以测量绝对核电荷半径，这是原子核的一个关键属性，它提供了关于核变形开始的信息，外来晕核的结构，以及核子之间的相互作用。在天体物理学中，核电荷半径是确定恒星元素丰度的重要参数，也是暗物质搜索的重要参数。在EBIT中Na-like和Mg-like HCI的原子光谱提供了一种新的方法来追求均方根核电荷半径的测量，补充了少数可用的基于核物理和原子物理的技术。除了强烈的电子-核重叠外，相对于中性原子或几次电离系统，高z离子中的相对论和量子电动力学（QED）效应也更为明显。实验精度由谱仪分辨率和Na/ mg类体系的高统计数据提供，辅以高精度的最先进的从头计算，从而允许研究原子结构效应，如超细分裂、核变形、核极化和高阶QED。该实验将测量一些核电荷半径不确定性最小的同位素（如钨和锇）之间的同位素位移，作为测试该技术极限和寻找BSM效应迹象的理想候选者。具有较大不确定度的同位素如铼的核电荷半径将以锇作为锚点进行。pi先前的工作已经在氙中证明了该方法，并将先前报道的铱同位素的不确定性降低了一个数量级。该奖项反映了美国国家科学基金会的法定使命，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。

This project is jointly funded by Atomic, Molecular, and Optical Experimental Physics, the Established Program to Stimulate Competitive Research (EPSCoR), and Experimental Nuclear Physics. When many of the outer electrons are removed from an atom, it becomes a highly charged ion. Such highly charged ions (HCI) are interesting as they have exotic properties compared to neutral atoms. In these ions, the remaining electrons are those that overlap significantly with the small central nucleus. Precision measurements of the light emitted as the electrons change orbits thus yields information about the nucleus. These include the finite nuclear charge radius, nuclear deformations, and magnetic properties. Using an electron beam ion trap (EBIT), this project aims to conduct an experimental study of HCI chosen to have simple, theoretically calculable electronic configurations in order to understand nuclear effects. By measuring the emitted radiation in the extreme-ultraviolet (EUV) and x-ray region, the PIs and their collaborators recently conducted a series of benchmark experiments using Na-like and Mg-like ions and determined the nuclear charge radii differences of high-Z isotopes. In the present project, they will expand these studies, investigate its limitations, and explore its sensitivity to beyond the standard model (BSM) physics. The study will also be used to improve the existing atomic theories of complex atomic systems. Graduate and undergraduate students will be involved in setting up the experiment, data collection, analysis, interpretation, scientific report writing, and presentation at conferences. The research work will integrate with the interdisciplinary educational programs taken by the students such as the “creative inquiry” program at Clemson University and the “Methods of Experimental Physics” at Appalachian State University. Students from underrepresented populations will be encouraged to join the research work and graduate students will be trained to mentor undergraduates.Only a few methods exist to measure the absolute nuclear charge radius, which is a key property of the nucleus that provides information about the onset of nuclear deformation, the structure of exotic halo nuclei, and the interaction between nucleons. In astrophysics, the nuclear charge radius enters in the determination of stellar elemental abundances and is an important parameter in dark matter searches. Atomic spectroscopy of Na-like and Mg-like HCI in an EBIT offers a new method to pursue the measurement of root-mean-square nuclear charge radii that supplement only a handful of available nuclear and atomic physics-based techniques. In addition to the strong electron-nuclear overlap, relativistic and quantum electrodynamics (QED) effects are also more pronounced in high-Z ions compared to neutral atoms or few-times ionized systems. The experimental precision provided by the spectrometer resolution and high statistics of the Na/Mg-like systems complemented by highly accurate state-of-the-art ab-initio calculations thus allows for the study of atomic structure effects such as hyperfine splitting, nuclear deformation, nuclear polarization, and higher-order QED. The experiment will measure the isotope shift between isotopes with some of the smallest nuclear charge radius uncertainties such as tungsten and osmium, serving as ideal candidates to test the limits of the technique and to look for the signs of BSM effects. Nuclear charge radii of isotopes with a large uncertainty such as rhenium will be conducted using osmium as an anchor. Prior work by the PIs have demonstrated the method in xenon and the reduction of the previously reported uncertainty of iridium isotopes by an order of magnitude.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.