权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

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。它已被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 对新物理搜索贡献的约束，以及强耦合和夸克质量等基本参数。然而，对于部分子分布函数 (PDF) 的 LQCD 计算，剩下的问题是 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。准 PDF 和 PDF 具有相同的红外物理特性，这是我们能够将这两个量联系起来的基本观察。然后，分解公式可以使用微扰理论从准 PDF 中提取 PDF，这种操作称为匹配。这个过程被称为大动量有效理论 (LaMET)，我们已使用它来首次重建物理点质量系综中核子内的 iso 向量 u(x)-d(x) 分布。它还可以深入了解核子海中轻夸克 d ̅(x)-u ̅(x) 的味道不对称性的本质。具体来说，对于风味不对称性，虽然可以在 LaMET 中计算，但由于多种因素的综合作用，几乎没有什么问题仍然妨碍对其得出明确的结论，包括：傅里叶变换少量点的问题，以及可能的体积和截止效应。最近，我们提出了另一种方法来测试风味不对称的起源，即使用 Δ^+ 重子。根据该提议，如果自发手性对称性破缺是测量到的不对称性的原因，那么与质子情况相比，d ̅(x)- u ̅(x) 在 Δ^+ 中应该得到强烈增强。计算和理解造成风味不对称的物理机制是我们建议的主要目标。