Precision Tests of Fundamental Physics via Light Pseudoscalar Mesons

了解夸克和胶子是如何将自己限制在构成元素的中子和质子中，以及寻找超越粒子物理学标准模型（SM）的新物理学，是物理学的两个前沿领域。该项目的主要目标是在杰斐逊实验室进行两个尖端实验，PrimEx-eta和JLab Eta工厂（JEF），以探索以前无法实现的灵敏度的基本主题。这些测量结果将揭示一些基本问题：量子色动力学约束的起源和动力学是什么？构成85%物质的暗物质的本质是什么？宇宙中观测到的物质和反物质不对称的原因是什么？该项目的范围包括硬件开发、实际实验性能和数据分析，将为一名博士后研究员和一批本科生提供高级培训。学生将获得动手实验技术，数据分析和计算的重要技能，以及批判性思维和解决问题的能力，以完成本科课程，并为STEM领域的职业生涯做好准备。在杰斐逊实验室工作的年轻研究人员（博士后和学生）将增加他们的经验和全球视野。该项目的女性PI起到了榜样作用，促进了STEM领域的多样性和包容性。PrimEx-eta实验将使用现有的GlueX仪器和由12x12排列的PbWO4晶体组成的新量热计，通过Primakoff效应以~3%的精度测量η辐射衰减宽度。它将解决以往使用Primakoff效应和e+e-碰撞的实验结果之间长期存在的差异（~3σ），并将提供轻夸克-质量比和η-η混合角的精确测定。JEF实验将测量各种η和η衰减，重点是稀有模式，产生一个干净的数据集，与所有以前的实验相比，背景抑制因子为两个数量级。除了基线GlueX设备外，JEF实验还需要升级的前向量热计（FCAL-II），在中心区域使用高粒度，高分辨率的PbWO4晶体核心，以最大限度地减少淋浴重叠并优化能量和位置的分辨率。从JEF实验收集的数据将为：(a)首次探索标量介子动力学在手性微扰理论中的作用提供灵敏的探针；(b)用η→3π Dalitz分布收紧了轻夸克质量比的不确定性；(c)寻找各种次gev暗规范玻色子候选者（包括矢量、标量和轴子样粒子），将现有的边界提高两个数量级以上，并补充目前世界范围内在高能对撞机和地下设施上的努力；(d)为违反c、守恒p的新力提供了最佳的直接约束。作为实验发言人，PI将在PrimEx-eta和JEF中发挥领导作用。项目负责人及其团队将：(1)分析PrimEx-eta第一阶段运行中收集的数据，准备并执行2021年秋季的第二阶段运行；(2)开发升级的FCAL-II，并为预计在2024年运行的JEF实验做准备；(3)继续负责维护和操作低粒度对光谱仪探测器，以控制d大厅的光子通量。该奖项反映了美国国家科学基金会的法定使命，并通过基金会的智力价值和更广泛的影响审查标准进行了评估，认为值得支持。

Understanding how quarks and gluons confine themselves into the neutrons and protons that make the elements, and searching for new physics beyond the Standard Model (SM) of particle physics are two frontiers in physics. The primary goal of this project is to perform two cutting-edge experiments, PrimEx-eta and JLab Eta Factory (JEF), at Jefferson Lab to explore both fundamental topics with sensitivities not previously achievable. These measurements will shed light on some fundamental questions: What is the origin and dynamics of Quantum Chromo Dynamic confinement? What is the nature of dark matter that constitutes 85% of matter and what is the cause for the asymmetry of matter and antimatter observed in the universe? The scope of this project, including hardware development, performance of the actual experiment and data analysis, will provide advanced training for a postdoctoral researcher and a group of undergraduate students. Students will acquire significant skills in hands-on experimental techniques, data analysis and computation, as well as critical thinking and problem-solving abilities to fulfill the undergraduate curricula and prepare them for careers in STEM fields. The opportunities for young researchers (postdoc and students) working at Jefferson Lab will enhance their experience and global perspectives. The female PI of this project serves as a role model and promotes diversity and inclusion in the STEM fields. The PrimEx-eta experiment will measure the η radiative decay width at ~3% precision via the Primakoff effect, using the existing GlueX apparatus with a new calorimeter consisting of 12x12 array of PbWO4 crystals. It will resolve a longstanding discrepancy (~3σ) between the previous experimental results using the Primakoff effect and e+e- collisions, and will offer accurate determinations of the light quark-mass ratio and the η-η' mixing angle. The JEF experiment will measure various η and ηꞌ decays with emphasis on rare modes, producing a clean dataset with background suppression of a factor of two orders of magnitude compared to all previous experiments. In addition to the baseline GlueX apparatus, the JEF experiment will require an upgraded forward calorimeter (FCAL-II) with a high-granularity, high-resolution PbWO4 crystal core in the central region that minimizes shower overlaps and optimizes the resolutions of energy and position. The data collected from the JEF experiment will provide sensitive probes to: (a) explore the role of scalar meson dynamics in chiral perturbation theory for the first time; (b) tighten the uncertainty in the light quark mass ratio by the η→3π Dalitz distributions; (c) search for various sub-GeV dark gauge boson candidates (including vectors, scalars and Axion-like particles) by improving the existing bounds by more than two orders of magnitude and is complementary to the ongoing worldwide efforts at high-energy collider and underground facilities; and (d) provide the best direct constraints for C-violating, P-conserving new forces. As an experiment spokesperson, the PI will play a leadership role in both PrimEx-eta and JEF. The PI and her team will: (1) analyze the data collected in the phase I run of PrimEx-eta, prepare and perform the phase II run in fall 2021; (2) develop an upgraded FCAL-II and prepare the JEF experiment for the anticipated run in 2024; (3) continue the service responsibility for maintaining and operating the low-granularity pair spectrometer detectors to control the photon flux in Hall D.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.