Hard Scattering Processes in QCD

核子（质子和中子）占宇宙可见物质质量的99%以上。它们由夸克和胶子组成，它们是量子色动力学（QCD）的基本粒子。核子的部分子结构编码在不同类型的部分子分布（PDFs）中，这些部分子分布可以从高能散射过程中提取，也可以从第一性原理计算（lattice-QCD）中获得。对于一个关键的PDF，核子横向性，在实验结果和晶格qcd之间存在显著和持久的不匹配。PI和他的合作者将重新审视和改进从实验中提取横向性，旨在从现象学中获得关于横向性的最新信息，并找到上述差异的来源。此外，PI将在微扰QCD中进行综合计算，这些计算需要从点阵QCD结果中获得两类重要的pdf，这两类pdf很难在实验中得到。PI还将仔细研究QCD能量动量张量，其中包含有关强子基本特性的信息，如质量和自旋，以及压力和剪切分布。此外，PI将指导研究生，为高中生和本科生开展外展活动，并为本科生和研究生提供强子物理暑期课程。该项目涉及强子物理中的三个主题。首先，PI将根据双强子产生的数据对核子的横向分布进行新的拟合。在新的首阶分析后，横向将在共线次首阶（NLO）框架中提取。这包括首次在微扰QCD中对电子-正电子湮灭、轻子-核子散射和质子-质子碰撞中相关的双强子观测值进行NLO计算。该研究可以为长期存在的实验数据和晶格qcd的横向信息之间的紧张关系提供新的线索。其次，PI将考虑欧几里得部分子相关器，以增强我们对扭曲-3 pdf和通过晶格- qcd的广义部分子分布的理解。具体来说，PI将在微扰QCD中计算相关的单环匹配系数，这对于将晶格-QCD的结果与人们感兴趣的光锥相关函数联系起来至关重要。第三，PI将考虑QCD能量动量张量来研究QCD中介子的质量分解，并探索强子内部的压力以及压力和剪切的分布。重点将放在适当的重整算符上，这是一个重要的主题，但迄今为止还没有得到太多的注意，特别是在压力和剪切分布方面。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。

Nucleons (protons and neutrons) make up more than 99% of the mass of the visible matter of the Universe. They are composed of quarks and gluons (partons), the fundamental particles of quantum chromodynamics (QCD). The parton structure of the nucleon is encoded in different types of parton distributions (PDFs), which can be extracted from high-energy scattering processes or obtained from first-principles calculations (lattice-QCD). For one crucial PDF, the nucleon transversity, a striking and persistent mismatch exists between results from experiment and lattice-QCD. The PI and his collaborators will revisit and improve the extraction of the transversity from experiment, aiming to obtain state-of-the-art information about the transversity from phenomenology and to find the source of the aforementioned discrepancy. Furthermore, the PI will perform comprehensive calculations in perturbative QCD that are needed to obtain, from lattice-QCD results, two important classes of PDFs that are difficult to address experimentally. The PI will also carefully study the QCD energy momentum tensor, which contains information about fundamental hadron properties like the mass and the spin, as well as pressure and shear distributions. Moreover, the PI will mentor graduate students, conduct outreach activities for high school students and undergraduates, and offer a summer program on hadronic physics for both undergraduate and graduate students.The project deals with three topics in hadronic physics. First, the PI will perform a new fit of the nucleon’s transversity distribution based on data for di-hadron production. After a new leading-order analysis, the transversity will be extracted in a collinear next-to-leading order (NLO) framework. This includes the first-ever NLO calculation, in perturbative QCD, of the relevant di-hadron observables in electron-positron annihilation, lepton-nucleon scattering and proton-proton collisions. The study can shed new light on the longstanding tension between information on the transversity from experimental data and from lattice-QCD. Second, the PI will consider Euclidean parton correlators to enhance our understanding of twist-3 PDFs and generalized parton distributions via lattice-QCD. Specifically, the PI will compute in perturbative QCD the relevant one-loop matching coefficients, which are crucial for relating results from lattice-QCD to the light-cone correlation functions one is interested in. Third, the PI will consider the QCD energy momentum tensor to study the mass decomposition of the pion in QCD, and to explore the pressure as well as the distributions of pressure and shear inside hadrons. A focus will be on properly renormalized operators, an important topic which so far has not received much attention, especially in relation to the pressure and shear distributions.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.