Mapping the Structure of Hadrons with Lattice QCD

了解可见物质的最内层结构是核物理学的一个重要研究领域。原子核的基本组成部分，质子和中子，是由强相互作用理论——量子色动力学（QCD）支配的基本夸克和胶子成分组成的。在过去的60年里，我们的知识有了很大的进步，但仍然存在许多难题：这些夸克和胶子是如何构成复合粒子的质量的？它们是如何促成自旋的？为什么由少一个夸克组成的介子，质量却少了大约10倍？许多实验设施也在竞相回答这些问题，比如杰斐逊实验室的加速器12gev项目和计划中的电子-离子对撞机。这些实验将促进核子和其他粒子的断层扫描。同时，高性能计算允许直接模拟QCD，提供有关难以通过实验获得的方面的信息。点阵QCD （LQCD）是一种利用超级计算机在四维时空晶格上直接模拟QCD的理论方法。利用这种技术，强子系统的性质可以从第一性原理（即从底层的夸克和胶子自由度）研究，具有完全可控的数值和系统不确定性。在过去的十年中，在生成QCD构型集合的有效算法和从LQCD相关函数中提取相关信息的工具的开发方面取得了重大进展。在某些情况下，LQCD计算已经达到了不仅补充，而且指导实验方案的水平。目前正在进行两个主要的研究方向。第一个是提供核子耦合和矩的精确LQCD计算，并充分研究晶格系统学，包括多个晶格间距和体积，直接在物理介子质量上。将精确的LQCD输入与正在进行和即将进行的精确低能量实验相结合，可以帮助为新物理学设定限制。第二个方向是利用准和伪pdf方法研究非单线态强子结构。重点是在大多数全局拟合中最大的理论不确定性之一，奇异-反奇异对称性的假设以及核子和介子的胶子结构。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。

Understanding the innermost structure of visible matter is an important research area in nuclear physics. The basic building blocks of the atomic nucleus, protons and neutrons, are composed of elementary quark and gluon constituents governed by the theory of the strong interaction, quantum chromodynamics (QCD). Our knowledge has advanced greatly over the last six decades but many puzzles remain: How do these quarks and gluons make up the masses of composite particles? How do they contribute to their spin? How can a pion, composed of one fewer quark, have mass roughly 10 times lower? Many experimental facilities are also racing to answer these questions, such as the Jefferson Lab accelerator 12-GeV program and the planned Electron-Ion Collider. These experiments will advance the tomography of nucleons and other particles. At the same time, high-performance computing allows the direct simulation of QCD directly, providing information about aspects that are hard to access via experiments. Lattice QCD (LQCD) is a theoretical method to directly simulate QCD on four-dimensional spacetime lattices using supercomputers. Using this technique, the properties of hadronic systems can be studied from first principles (that is, from the underlying quark and gluon degrees of freedom) with fully controllable numerical and systematic uncertainties. In the past decade, there has been significant progress in the development of efficient algorithms for generating ensembles of QCD configurations and tools for extracting relevant information from LQCD correlation functions. In some cases, LQCD calculations have reached a level where they not only complement, but also guide experimental programs. Two main research directions are being pursued. The first is to provide precision LQCD calculations of nucleon couplings and moments with full studies of lattice systematics, including multiple lattice spacings and volumes, directly at physical pion mass. Combining precision LQCD inputs with ongoing and upcoming precision low-energy experiments can help set limits for new physics. The second direction is to investigate non-singlet hadron structure using quasi- and pseudo-PDF methods. Focus is on one of the biggest theoretical uncertainties in most global fits, the assumption of strange-antistrange symmetry and the gluon structure of nucleons and mesons.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.