Intermediate Energy Nuclear Physics with Electromagnetic Probes at Jefferson Lab

目前的NSF拨款主要资助RPI小组参与托马斯杰斐逊国家加速器设施的物理项目，在那里它是CLAS合作的成员。这个实验项目的目标是了解质子和中子的组成，并对它们进行成像。质子和中子通常被称为核子，它们构成了目前宇宙中几乎所有可见的物质。核子是由非常复杂的夸克阵列组成的，这些夸克被浸入被称为胶子的强核场中。使用的主要仪器是CLAS光谱仪，其中来自杰斐逊实验室加速器的电子束撞击目标质子。大多数情况下，目标是以液氢原子的形式存在。RPI小组关注的实验是这样的：电子束中的一个电子撞击并散射掉一个质子，传递给质子的部分能量要么产生一个光子（一种电磁辐射量子），要么产生一个介子（一种由夸克和反物质夸克对组成的粒子）。通过研究这一反应，当散射电子的能量和方向发生变化时，该小组试图获得质子中夸克分布的三维图像，这是迄今为止从未完成的。在此拨款期间，该小组将继续研究新的CLAS光谱仪，称为CLAS12，这是杰斐逊实验室正在进行的项目的一部分，旨在使电子束的能量加倍。RPI特别贡献的CLAS12光谱仪的组件被称为高阈值切伦科夫计数器（HTCC），它将用于识别散射电子。这是除了首席研究员作为第12类指导委员会主席在升级中扮演的更一般的角色之外。RPI是一所以技术为基础的大学，其主要目标是为社会最先进的技术需求培养未来的科学家和工程师。本研究中实验的复杂性要求开发和使用最先进的科学设备和计算技术。RPI的研究生和本科生，以及博士后助理，以这样或那样的方式参与这样的项目，并在目前的情况下直接开展大部分实验项目的直接工作，使他们成为技术竞争社会的科学和工程领导者。

The present NSF grant primarily funds the RPI group's participation in the the physics program of the Thomas Jefferson National Accelerator Facility, where it is a member of the CLAS Collaboration. The experimental program's goal is to learn about and image the composition of protons and neutrons - generically called nucleons - which comprise nearly all the currently visible matter in the universe. Nucleons are composed of very complicated arrays of quarks immersed in the strong nuclear fields called gluons. The main instrument used is the CLAS spectrometer, inside of which a beam of electrons from the Jefferson Lab accelerator impinges upon a target of protons. Most often the target is in the form of liquid hydrogen atoms. The experiments in which the RPI group are focusing are those in which an electron in the beam strikes and scatters off a proton and part of the energy imparted to the proton produces either a single photon (a quantum of electromagnetic radiation), or a single meson, which is a particle consisting of a quark and antimatter quark pair. By studying this reaction as the imparted energy and direction of the scattered electron is varied, the group seeks to obtain a three dimensional image of the distributions of the quarks in the proton, which has never yet been accomplished. During this grant period the group will continue work on a new CLAS spectrometer, called CLAS12, which is part of the ongoing project at Jefferson Lab to double the energy of the electron beam. The component of the CLAS12 spectrometer on which the RPI is specifically contributing is called a high threshold Cherenkov counter (HTCC), which will be used to identify the scattered electrons. This is in addition to the more general role the Principal Investigator plays in the upgrade as chairman of the CLAS12 steering committee. RPI is a technology based university whose primary goal is to prepare future scientists and engineers for the most advanced technological demands of society. The complexity of the experiments in this research require the development and use of the most advanced scientific equipment and computational techniques. RPI graduate and undergraduate students, as well as post-doctoral associates, participate one way or another in programs such as this, and in the present case directly carry out most of the direct work on the experimental program, enabling them to become the scientific and engineering leaders of a technologically competitive society.