Investigating the Electromagnetic Structure of the Nucleon and Light Nuclei at Jefferson Lab

该研究项目的主要目标是继续在弗吉尼亚州纽波特纽斯的托马斯·杰斐逊国家加速器设施（“杰斐逊实验室”）进行合作，该设施专门用于利用高能电子束探测核子的结构。这项工作将与杰斐逊实验室A厅的超级大咬光谱仪（SBS）合作完成。在此拨款期间，杰斐逊实验室将从过去的过渡“升级期”阶段——将光束能量从6 GeV升级到12 GeV——开始使用专门为更高能量设计和建造的设备。该提案包括一项计划，以确保持续的科学贡献和学生培训早期运行的a厅实验（实验不仅关注核子结构，而且还关注轻核-特别是triton三核子系统），但主要重点仍然是与一系列特定的后续运行SBS实验相关的准备/开发项目，这些实验将探测核子结构功能在非常高的动量转移。这个项目的所有方面的驱动物理目标都与提高对从大约1到几个费米（强子自由度最合适）的相对较大距离尺度的“强（非微扰）QCD”制度到更短距离尺度的“微扰QCD”制度的转变的理解有关。******Sarty已经与杰斐逊实验室的A厅合作了二十年，在过去几年实验室升级的设备开发中，Sarty和他的学生为A厅的SBS实验组的设计/测试项目做出了贡献。SBS实验设计用于探测高动量转移下的核子结构；该组的标志性实验是E12-07-109（“使用反冲极化法测量13和15 GeV/c^2下的大接受质子形状因子比”）。这组SBS实验需要建造新的设备- -光谱仪、量热计和探测器- -这些将在这一拨款期间由合作完成。Sarty的小组在准备SBS探测系统的一部分方面发挥了主导作用：一个基于闪烁体的坐标探测器（CDet），为散射电子探测提供所需的快速定时和精确位置——这是E12-07-109实验的高辐射背景环境所需要的关键方面。CDet将由0.5毫米高（4厘米厚）的闪烁体条组成，堆叠形成大约3米x 1米大小的两个平面，总共有2352个读出通道；Sarty的小组将继续其工作，以确保CDet的构建和一个适当的数据采集系统准备好，当在授权期结束时需要用于SBS核子结构实验时。

The primary objective of this research project is to continue collaborative efforts at the Thomas Jefferson National Accelerator Facility ("Jefferson Lab") in Newport News, Virginia, which are specifically aimed at probing the structure of the nucleon using a high energy electron beam. This work will be accomplished in collaboration with the Super BigBite Spectrometer (SBS) Collaboration in Hall A at Jefferson Lab. During this grant period, Jefferson Lab will be emerging from the past transition "upgrade period" phase - having upgraded the beam energy from 6 GeV to 12 GeV - and beginning to utilize equipment specifically designed and built for the higher energy. This proposal includes a plan to ensure continued scientific contributions and student training with the early-running Hall A experiments (experiments focusing not only on nucleon structure, but also on that of light nuclei - particularly the triton three-nucleon system), but with primary emphasis remaining on preparation/development projects associated with a series of specific later-running SBS experiments that will probe nucleon structure functions at very high momentum transfers. The driving physics goals of all aspects of this project are related to improving understanding of the transition from the 'strong (non-perturbative) QCD' regime of relatively large distance scales of approximately 1 to a few fermis (where hadronic degrees of freedom are most appropriate), to the 'perturbative QCD' regime of much shorter distance scales.******Sarty has been working with Jefferson Lab's Hall A Collaboration for two decades, and during the past few years of equipment development for the lab's upgrade, Sarty and his students contributed to design/testing projects for Hall A's SBS group of experiments. The SBS experiments are designed to probe nucleon structure at very high momentum transfer; the hallmark experiment of this group being E12-07-109 ("Large Acceptance Proton Form Factor Ratio Measurements at 13 and 15 GeV/c^2 using Recoil Polarization Method"). This SBS group of experiments requires the construction of new equipment - a spectrometer, calorimeters, detectors - which will be completed by the collaboration during this granting period. Sarty's group has taken a lead role in preparing one part of the SBS detection system: a scintillator-based Coordinate Detector (CDet) to provide required fast timing and accurate position for the scattered electron detection - critical aspects needed for the very high radiation background environment of the E12-07-109 experiment. The CDet will consist of 0.5mm tall (4cm thick) scintillator strips, stacked to form two planes roughly 3m x 1m in size, for a total of 2352 channels of readout; Sarty's group will continue its work to ensure the CDet is constructed and an appropriate data acquisition system is ready for use when it is needed for SBS nucleon structure experiments at the end of the granting period.