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

合作研究：RUI：PM：高阻抗高带电离子探测核电荷半径、QED 和标准模型

• 批准号: 2309274
• 负责人: Roshani Silwal
• 金额: $ 20.8万
• 依托单位: Appalachian State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-01 至 2026-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2309274&HistoricalAwards=false
• 关键词: Collaborative; Research; RUI; PM; Highly

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.

该项目由原子、分子和光学实验物理、刺激竞争研究的既定计划(EPSCoR)和实验核物理共同资助。当许多外层电子从一个原子上移走时，它就变成了一个高带电离子。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中央小核显著重叠的电子。对电子改变轨道时发出的光进行精确测量，从而得到有关原子核的信息。这些参数包括有限的核电荷半径、核形变和磁性。利用电子束离子陷阱(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，以便了解核效应。通过测量极端紫外线(EUV)和x射线区域的辐射，PI和他们的合作者最近使用类钠和类镁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。在本项目中，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。这项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的建立、数据收集、分析、解释、科学报告的撰写和在会议上的陈述。研究工作将与学生们采取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”项目。来自代表性不足人群的学生将被鼓励加入研究工作，研究生将被培训为本科生导师。目前只有几种方法可以测量核电荷绝对半径，这是原子核的一个关键属性，它提供了关于原子核形变开始、奇异晕核结构和核子之间相互作用的信息。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，也是暗物质研究的重要参数。EBIT中类钠和类镁HCI的原子光谱学提供了一种新的方法来测量均方根核电荷半径，这只是对现有的几种基于核和原子物理的技术的补充。除了强烈的电子-核重叠，相对论和量子电动力学(QED)效应在高Z离子中也比中性原子或少数几次电离系统更加明显。由能谱仪分辨率和高统计量的类钠/镁体系提供的实验精度，再加上高精度的从头计算，因此允许研究原子结构效应，如超精细分裂、核变形、核极化和高阶QED。这项实验将测量具有最小核电荷半径不确定度的同位素之间的位移，如钨和Os，这是测试该技术的局限性和寻找BSM效应迹象的理想候选者。具有很大不确定性的同位素，如Re的核电荷半径将使用Os作为锚进行测量。PIS之前的工作已经证明了该方法在氙气中的应用，并将以前报道的Ir同位素的不确定度降低了一个数量级。这一奖励反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。