Heavy Quarkonia in Lattice QCD with Anisotropic Highly Improved Staggered Quarks

强大的作用力将称为夸克的基本粒子结合成质子和中子，而后者又结合成原子核，这是在宇宙中所有尺度上观察到的物质的基本组成部分。量子色动力学（QCD）是20世纪发展起来的一种量子场论，它成功地描述了这些基本组分之间的强相互作用。QCD的预测已经以惊人的实验精度得到了验证。在正常条件下，孤立的夸克是观察不到的——它们被限制在质子和中子等复合物体中。然而，当强相互作用的物质被加热到非常高的温度（大约是太阳核心温度的百万倍）或压缩到非常高的密度（据推测在中子星的核心达到的密度）时，一种叫做夸克-胶子等离子体（QGP）的物质的新阶段就形成了。该项目将从第一性原理QCD计算中研究QGP的性质，特别是重夸克的复合态如何响应QGP介质以及在极短距离尺度下强作用力的行为（QGP显微镜）。这些研究将为布鲁克海文国家实验室的相对论重离子对撞机和欧洲核研究组织的大型强子对撞机的实验结果提供理论理解和解释。晶格QCD模拟是通过蒙特卡罗采样四维时空网格上基本场的最可能配置并计算其上的物理观测值来实现的。重夸克束缚态的物理信息编码在它们的谱函数中。为了从欧几里得晶格相关函数中可靠地提取谱函数，PI将开发一种各向异性高改进交错夸克（aHISQ）的形式，其中时空网格是各向异性的，在时间方向上具有更高的分辨率。该项目将为动态aHISQ夸克的晶格QCD模拟开发必要的算法和计算机代码，并将生成一个公开可用的高质量aHISQ集合库，其中包含各种晶格间距和各向异性的场构型，特别是用于重夸克谱函数重建。重夸克将被纳入非相对论性QCD （NRQCD）框架。非常高的各向异性与动态aHISQ夸克相结合，将为可靠地提取具有充分评估的统计和系统不确定性的谱函数铺平道路。PI将指导参与研究的博士生，并参与公共宣传活动。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。

The strong force binds elementary particles called quarks into protons and neutrons and the latter into atomic nuclei that are the fundamental building blocks of the matter observed in the Universe at all scales. These strong interactions of the elementary constituents are successfully described by Quantum Chromodynamics (QCD) - a quantum field theory developed in the course of 20th century. Predictions of QCD have been verified with amazing experimental precision. Under normal conditions isolated quarks are not observed - they are confined in composite objects like protons and neutrons. However, when strongly interacting matter is heated up to very high temperatures (about million times the temperature in the core of the Sun) or compressed to very high densities (the ones presumably achieved at the core of a neutron star), a novel phase of matter called Quark-Gluon Plasma (QGP) is formed. This project will study from first-principle QCD calculations the properties of QGP, in particular, how composite states of heavy quarks respond to the QGP medium and how the strong force behaves at very short distance scales (microscopy of QGP). These investigations will provide theoretical understanding and interpretation of the experimental results from the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory and Large Hadron Collider at the European Organization for Nuclear Research.Lattice QCD simulations are performed by Monte Carlo sampling the most probable configurations of fundamental fields on the four-dimensional space-time grid and computing physical observables on them. The physical information about heavy-quark bound states is encoded in their spectral functions. For reliable extraction of the spectral functions from Euclidean lattice correlation functions, the PI will develop a formalism of anisotropic Highly Improved Staggered Quarks (aHISQ), where the space-time grid is anisotropic with higher resolution in the temporal direction. The project will develop necessary algorithms and computer codes for lattice QCD simulations with dynamical aHISQ quarks and will generate a publicly available library of high-quality aHISQ ensembles of field configurations at various lattice spacings and anisotropies specifically for heavy quarkonia spectral function reconstruction. The heavy quarks will be included in the framework of Non-Relativistic QCD (NRQCD). Very high anisotropies combined with dynamical aHISQ quarks will pave the way to reliable extraction of the spectral functions with fully assessed statistical and systematic uncertainties. The PI will mentor doctorate students involved in the research as well as engage in public outreach activities.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.