RUI: Probing the Structure of Nucleons in Omega Meson Electroproduction

准确理解原子核内部强力是如何产生的，是当今核物理学家面临的最大智力挑战之一。强作用力产生核力，将质子和中子束缚在原子核内。这种强作用力是由被称为胶子的粒子交换介导的。正是胶子的相互作用占据了核子的大部分质量。核子是质子或中子的总称。核子是由三个价夸克嵌在泡沫般的胶子海洋中形成的。然而，我们对质子和中子是如何由夸克和胶子组成的了解，充其量也只是初步的。一个高能粒子，如电子，可以直接与原子核内的一个价夸克相互作用，使夸克发生自旋翻转或赋予夸克轨道或径向激发。夸克处于高能态时，受激发的核子质量就会变大。这些激发态被称为核子共振（N*s），存在的时间极短——大约是万亿分之一秒（10−24秒），然后会衰变成其他粒子。产生的粒子的类型以及它们在空间中的分布提供了关于质子构成的关键信息。拉马尔大学是一所本科院校。在过去的二十年中，PI已经建立了让本科生参与他的研究项目的良好记录，并且这种做法将在该奖项的支持下继续下去。杰斐逊实验室（弗吉尼亚州纽波特纽斯）和ELSA（德国波恩）对理解核子共振的这些基本测量，以及该奖项的强大教育重点，与核科学咨询委员会2015年长期计划的关键目标保持一致，从而服务于国家利益。这个研究项目是通过在杰弗逊实验室和ELSA使用一束线性偏振光子和/或极化电子来研究核子的基本性质和结构。强核相互作用导致了从夸克与胶子的结合、夸克与无色强子的结合、核子与原子核的结合以及大原子核的集体行为等大距离尺度上的现象。这个研究小组寻求以下问题的答案：当海夸克和胶子的贡献最小时，价夸克如何自组装，胶子如何附着在夸克上以增加当前夸克的质量到组成夸克的质量，以及夸克如何在核子内部共振以形成夸克的激发态组装。PI和他的本科生小组旨在了解夸克和胶子集合的涌现行为和结构。这些研究的探针将是介子。通过欧米茄介子的清晰和明确的信号探测N*s的结构有很大的发现潜力。此外，重子共振作为动量转移的函数通过欧米茄模式衰减的数据也非常缺乏。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。

Understanding exactly how the strong force is generated inside the nucleus is one of the greatest intellectual challenges facing nuclear physicists today. The strong force gives rise to the nuclear forces that bind protons and neutrons together inside the nucleus. The strong force is mediated by the exchange of particles known as gluons. It is this gluon interaction that accounts for most of mass of the nucleon. The nucleon is the general term for either a proton or a neutron. Nucleons are formed of three valence quarks embedded in a frothing sea of gluons. Our knowledge of how protons and neutrons are constructed from their quark and gluon constituents, however, is rudimentary at best. An energetic particle, such as an electron, incident on a nucleon can interact directly with one of the valence quarks inside, causing the quark to undergo a flip in spin or endowing the quark with an orbital or radial excitation. With a quark in a higher energy state, the excited nucleon becomes more massive. These excited states are called nucleon resonances (N*s) and exist for the briefest of moments – on the order of a trillionth of a trillionth of a second (10−24 s), and thence will decay into other particles. The types of particles produced and how they are distributed in space provides key information on the make-up of the proton. Lamar University is a Primarily Undergraduate Institution. Over the course of the past two decades, the PI has established a strong record of involving undergraduate students in his research program, and that practice will continue with support from this award. These fundamental measurements on understanding nucleon resonances at Jefferson Lab (Newport News, Virginia) and at ELSA (Bonn, Germany), along with the strong educational focus of this award, are in keeping with the key objectives of the Nuclear Science Advisory Committee’s 2015 Long-Range Plan and thereby serve the national interest.This research program is a study of the fundamental properties and structure of nucleons by using a beam of linearly-polarized photons and/or polarized electrons at Jefferson Lab and at ELSA. The strong nuclear interaction is responsible for phenomena over a large distance scale from the binding of quarks by gluons, the combinations of quarks into colorless hadrons, the binding of nucleons into nuclei, and the collective behavior of large nuclei. This research group seeks answers to questions such as how valence quarks self-assemble when sea quark and gluon contributions are minimal, the nature of how gluons attach to quarks to increase the mass of current quarks to that of constituent quarks, and how quarks resonate inside the nucleon to form excited assemblies of quarks. The PI and his group of undergraduate students aim to understand the emergent behavior and structure from assemblies of quarks and gluons. The probe for these studies will be the omega meson. There is great discovery potential in probing the structure of N*s through the clean and unambiguous signal of the omega meson. Moreover, there is a significant dearth of data of baryon resonances decaying through the omega mode as a function of momentum transfer.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.