Studies of the Structure of the Nucleon

从最基本的层面理解宇宙这一物理学目标的进步表明，物质是由一组基本粒子组成的，这些基本粒子结合起来形成其他粒子，这些粒子聚集在一起产生我们周围所认识的结构。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，它们给这些粒子提供了子结构。这个项目的目标是确定质子和中子结构的各个方面，以及当质子和中子被放置在原子核中时，这种结构是如何受到影响的。实验的重点是夸克如何在空间和动量中分布。一个持续存在的谜题是，当用氢原子和它的对应物——介子-氢来测量时，质子的大小是否不一样。在这种情况下，氢原子中的电子被它更重的表亲——介子所取代。该项目包括测量质子的电子和介子散射，以提供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青年科学家提供了在现代科学实验的国际合作中工作的经验和培训，并提供了最先进的技术。这项提议的主要目的是研究核子的结构。正在进行的Fermilab SEAQUEST实验利用drerel - yan截面确定了核子中反d与反u夸克的比值作为夸克动量的函数，研究了横向动量分布，研究了EMC效应，研究了冷核物质中的夸克能量损失，并研究了在质量较高但与普通物质耦合常数较低的参数区域中暗光子存在的可能性。Fermilab MINERvA实验通过从质子和原子核散射少量GeV中微子，提供了核子和核结构的互补视图。在杰斐逊实验室，氚靶实验将于2017年进行。MARATHON实验通过比较3H和3He上电子的深度非弹性散射，提供了高x下质子和中子F2结构函数的比例信息，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（Paul Scherrer Institute）的缪斯实验（MUSE）正在进行一项新实验的初步阶段，该实验旨在从质子中弹性地散射介子和电子，目的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when measured with atomic hydrogen and its counterpart, muonic-hydrogen, where the electron in the hydrogen atom has been replaced by its heavier cousin, the muon.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.