Studies of hadronic structure using electromagnetic probes

使用电磁探针研究强子结构

• 批准号: SAPIN-2021-00026
• 负责人: Huber, Garth
• 金额: $ 8.01万
• 依托单位: University of Regina
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=743103
• 关键词: Studies; hadronic; structure; using; electromagnetic

One of the central problems of modern physics research concerns our understanding of the building blocks of the atomic nucleus - the protons, neutrons, and other particles (mesons) that bind them. Notable discoveries have indicated that these particles consist of yet more fundamental constituents, the quarks and gluons. While a very good theoretical framework (called Quantum Chromo-Dynamics, or QCD) is able to accurately describe how quarks and gluons interact at extremely high energies (or, equivalently, when the quarks are very close together), it has been very difficult to apply QCD to lower energy (longer distance) phenomena. One of the obstacles to our improved comprehension has been a lack of quality data, particularly for the Deep Exclusive Reactions, which provide the clearest picture of the inner workings of QCD. Jefferson Lab enables these studies with its continuous, high luminosity electron beams, and detectors with good particle identification and reproducible systematics. 1. p+ and K+ Elastic Form Factors (Fp, FK): The internal structures of the two lightest mesons are parametrized by their form factors, and are critical hadronic structure quantities to understand. The p+ form factor offers our best hope of directly observing QCD's transition from strong-confinement at long-distance scales to asymptotic-freedom at short-distances. The K+, where the d quark is replaced with an s quark, provides a vital second study case.  Objectives: (i) establish the reliability of the extraction of the meson form factors from electroproduction data over a broad kinematic range, (ii) obtain high quality form factor measurements to high momentum transfer. The K+ data were acquired in 2018-19, while the p+ data were partly acquired in 2019, with the bulk to be acquired in 2021, 2023. The data are being analyzed by four Regina PhD students. 2. Unique Access to u-Channel Physics: Backward-angle meson electroproduction is anticipated to offer unique access to the three quark plus sea component of the nucleon wave function. We pioneered a new technique, which demonstrated the feasibility of high quality measurements in this previously unexplored region. Our upcoming experiment will take ?, ? and f data with goals: (i) establish existence of a backward-angle cross section peak for multiple reaction channels; (ii) extract the separated cross sections over a wide kinematic range; and (iii) establish whether the collinear factorization scheme is valid. 3. Study of Generalized Parton Distributions (GPDs):  SoLID (Solenoidal Large Intensity Device) will allow new data to be acquired on GPDs, "universal objects" providing a comprehensive description of the quark and gluon structure of the nucleon. Regina students will participate in SoLID detector construction and testing, planned for 2022-25, and contribute to our experiment probing the poorest known GPD, E-tilde. Funds are requested for Jefferson Lab fieldwork, PhD student and PDF salary support.

现代物理学研究的中心问题之一涉及到我们对原子核的组成部分——质子、中子和其他结合它们的粒子（介子）的理解。一些值得注意的发现表明，这些粒子由更基本的成分——夸克和胶子组成。虽然一个非常好的理论框架（称为量子色动力学，或QCD）能够准确地描述夸克和胶子如何在极高的能量下相互作用（或者，当夸克非常接近时），但将QCD应用于较低能量（较长的距离）现象是非常困难的。阻碍我们提高理解的障碍之一是缺乏高质量的数据，特别是关于深度独占反应的数据，这些数据提供了QCD内部工作的最清晰图像。杰斐逊实验室通过其连续的、高亮度的电子束和具有良好的粒子识别和可复制系统的探测器，使这些研究成为可能。1. p+和K+弹性形状因子（Fp， FK）：两个最轻介子的内部结构是由它们的形状因子参数化的，是理解的关键强子结构量。p+形状因子提供了我们直接观察QCD从远距离尺度的强约束到短距离渐近自由的转变的最大希望。在K+中，d夸克被s夸克取代，这提供了第二个重要的研究案例。目标：(i)建立在广泛的运动学范围内从电生产数据中提取介子形状因子的可靠性，（ii）获得高质量的形状因子测量以实现高动量传递。K+数据是在2018-19年获得的，而p+数据是在2019年获得的，大部分数据将在2021年和2023年获得。这些数据正在由四名里贾纳大学的博士生进行分析。2. u通道物理的独特途径：反向角度介子电产生预计将为核子波函数的三夸克加海分量提供独特的途径。我们开创了一项新技术，证明了在这个以前未开发的地区进行高质量测量的可行性。我们即将进行的实验将采取？， ？ (1)建立多反应通道后角截面峰的存在性；（ii）在大的运动范围内提取分离的横截面；(3)建立共线分解方案是否有效。3. 广义部子分布（GPDs）的研究：SoLID（螺线管大强度装置）将允许获得关于GPDs的新数据，“通用对象”提供核子的夸克和胶子结构的全面描述。里贾纳的学生将参与固体探测器的建设和测试，计划在2022-25年进行，并为我们探测已知最穷的GPD E-tilde的实验做出贡献。资金要求杰斐逊实验室实地考察，博士生和PDF工资支持。