Studies of the Structure of the Nucleon

在最基本的层面上理解宇宙的物理学目标的进展表明，物质是由一组基本粒子组成的，这些粒子联合收割机形成其他粒子，这些粒子聚集在一起产生我们周围认识的结构。例如，原子核是由质子和中子的混合物形成的。 这些质子和中子是由夸克和胶子组成的，它们是这些粒子的子结构。该项目的目标是确定质子和中子的结构方面，以及当放置在原子核中时如何影响这种结构。实验的重点是夸克在空间和动量中的分布。一个持续的难题是，当用原子氢和它的对应物μ介子氢测量时，质子的大小是否不一样，其中氢原子中的电子被它更重的表亲μ介子取代。该项目包括测量质子的电子和μ子散射，以提供对质子半径的独立测量。除了该项目的直接科学目标外，这些实验还为学生和年轻科学家提供了在现代科学实验国际合作中工作的经验和培训，以及最先进的技术。正在进行的费米实验室SEAQUEST实验使用Drell-Yan截面来确定核子中反d夸克与反u夸克的比例作为夸克动量的函数，研究横向动量分布，研究EMC效应，研究冷核物质中的夸克能量损失，并研究在较高质量但与普通物质的耦合常数较低的参数区域中暗光子的可能存在。费米实验室的MINERvA实验通过从质子和原子核中散射少量GeV的中微子，提供了对核子和原子核结构的补充观点。在杰斐逊实验室，氚靶实验将于2017年进行。马拉松实验通过比较电子在3 H和3 He上的深度非弹性散射，提供了关于质子和中子F2结构函数在高x下的比率的信息，测试了几十年前的微扰量子色动力学模型计算。瑞士保罗·谢勒研究所的MUSE实验是一个新的实验，旨在从质子中弹性散射μ子和电子，目前正在进行初步阶段，目标是测量质子中的电荷分布。

Advances in the physics goal of understanding the universe at its most fundamental level have shown that matter is composed of a set of fundamental particles that combine to form other particles that group together to generate the structures that we recognize around us. For example, the nucleus of an atom is formed from a mixture of protons and neutrons. These protons and neutrons are made from constituents, called quarks and gluons, which give substructure to these particles. The goal of this project is to determine aspects of the structure of the proton and neutron, and how this structure is affected when placed in the nucleus. The experiments focus on how the quarks are distributed in space and in momentum. An on-going puzzle is whether the proton size is not the same when measured with atomic hydrogen and its counterpart, muonic-hydrogen, where the electron in the hydrogen atom has been replaced by its heavier cousin, the muon. The project includes measurement of electron and muon scattering from protons to provide an independent measurement of the proton radius. In addition to the direct scientific goals of the project, the experiments provide students and young scientists experience and training in working in the international collaborations of modern scientific experiments, with state of the art technology.The primary goal of this proposal is study the structure of the nucleon. The ongoing Fermilab SEAQUEST experiment uses Drell-Yan cross sections to determine the ratio of anti-d to anti-u quarks in the nucleon as a function of quark momentum, to study transverse momentum distributions, to investigate the EMC effect, to study quark energy loss in cold nuclear matter, and to investigate the possible existence of dark photons in a parameter region of higher mass but lower coupling constant to ordinary matter. The Fermilab MINERvA experiment provides a complementary view of nucleon and nuclear structure by scattering few GeV neutrinos from protons and from nuclei. At Jefferson Lab, experiments on tritium targets will be run in 2017. The MARATHON experiment, through a comparison of deep inelastic scattering of electrons on 3H to 3He, provides information on the ratio of the proton and neutron F2 structure functions at high x, testing decades old perturbative quantum chromodynamics model calculations. The preliminary phases of creating a new experiment to elastically scatter muons and electrons from the proton, the MUSE experiment at the Paul Scherrer Institute in Switzerland, are in progress, with the goal of measuring the distribution of charge in the proton.