Parton Distributions from Lattice QCD and Flavor Symmetry Breaking in the Delta Sea

三角洲海中晶格 QCD 的帕顿分布和风味对称性破缺

基本信息

批准号：
392578569
负责人：
Dr. Fernanda Monti Steffens
金额：
--
依托单位：
Helmholtz-Institut für Strahlen- und Kernphysik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2017
资助国家：
德国
起止时间：
2016-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/392578569?language=en
关键词：
Parton Distributions Lattice QCD Flavor

项目摘要

Lattice Quantum Chromodynamics (LQCD) provides a generic, non-perturbative way to solving QCD at low energies. It has been used to study the various aspects of nuclear and particle physics, e.g. hadron scattering and resonance phenomena, hadronic matrix elements for electroweak decays, chiral dynamics and anomaly and constraints of QCD contributions for new-physics search, as well as fundamental parameters such as the strong coupling and quark masses. However, for a LQCD computation of parton distribution functions (PDFs), a remaining problem is that LQCD is formulated on Euclidean spacetime while the PDFs are light-cone dominated. In 2013, Ji proposed that instead of computing light-cone correlations directly, one should compute purely spatial correlations, whose Fourier transform are usually referred to as quasi-PDFs. Quasi-PDFs and PDFs possess the same infrared physics, which is the fundamental observation that allows us to relate both quantities. A factorization formula then makes it possible to extract the PDFs from the quasi-PDFs, an operation called matching, using perturbation theory. This procedure is known as large-momentum effective theory (LaMET) and it has been used by us to make a first reconstruction of the iso-vector u(x)-d(x) distribution within a nucleon at a physical point mass ensemble. It may, also, offer an insight into the nature of the flavor asymmetry for the light quarks in the nucleon sea, d ̅(x)-u ̅(x). Specifically, for the flavor asymmetry, although it can be computed in LaMET, few issues still prevent firm conclusions on it, because of a combination of factors, including: the problem of Fourier transforming a small number of points, and possible volume and cut-off effects. Recently, we proposed an alternative way to test the origin of the flavor asymmetry, using the Δ^+ baryon. According to this proposal, if spontaneous chiral symmetry breaking is responsible for the measured asymmetry, then d ̅(x)- u ̅(x) should be strongly enhanced in the Δ^+, as compared to the proton case. The computation and the understanding of the physical mechanism responsible for the flavor asymmetry is the main objective of our proposal.

晶格量子色动力学 (LQCD) 提供了一种通用的、非微扰的方法来求解低能 QCD，它已用于研究核物理和粒子物理的各个方面，例如强子散射和共振现象、电弱衰变的强子矩阵元素、手性动力学和异常以及 QCD 对新物理搜索的贡献的约束，以及强耦合和夸克质量等基本参数。在计算部分子分布函数（PDF）时，剩下的一个问题是，LQCD 是在欧几里德时空上制定的，而 PDF 是光锥主导的。2013 年，Ji 提出，不应直接计算光锥相关性，而应计算纯粹的空间相关性。，其傅里叶变换通常被称为准 PDF 和 PDF 具有相同的红外物理特性，这是我们将两个量关联起来的基本观察。使得可以使用微扰理论从准 PDF 中提取 PDF，这一过程称为大动量有效理论 (LaMET)，我们已使用它来对 iso 进行首次重建。 -向量 u(x)-d(x) 在物理点质量系综上的核子内分布，它还可以提供对核子海中轻夸克 d 的味道不对称性质的深入了解。具体来说，对于味道不对称性，尽管可以在 LaMET 中计算，但由于多种因素的结合，很少有问题仍然妨碍对其得出明确的结论，包括：傅里叶变换问题。最近，我们提出了另一种方法来测试味道不对称性的起源，根据这个建议，自发手性对称性破缺是造成这种现象的原因。测量的不对称性，那么与质子情况相比，d ̅(x)- u ̅(x) 应该在 Δ^+ 中得到强烈增强。计算和理解造成风味不对称的物理机制是主要目标。我们的建议。