Nucleon Spin Structure Studies Using Parity Violating and Inelastic Electron Scattering

利用宇称破坏和非弹性电子散射进行核子自旋结构研究

• 批准号: 9901428
• 负责人: Todd Averett
• 金额: $ 12万
• 依托单位: College of William and Mary
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-08-01 至 2001-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9901428&HistoricalAwards=false
• 关键词: Nucleon; Spin; Structure; Studies; Using

9901428AverettAn experimental program is underway to study the structure of thenucleon in terms of quark degrees of freedom at the Thomas JeffersonNational Accelerator Facility (Jefferson Laboratory). This researchwill be carried out in two distinct experimental programs. The firstis the so-called ``G0'' experiment which will use parity violating electron scattering to precisely determine the weak elastic form factors of the proton. From this measurement, one can extract the strange electric and magnetic form factors which are directly related to the charge and current distributions of the strange quarks within the nucleon. To achieve the goal of high precision and broad kinematic coverage of this experiment, a dedicated large acceptance and liquid hydrogen target are being constructed. Design, prototype studies, and final construction of the detector is the shared responsibility of the Electroweak Spin Physics Group (Finn et al.) and myself at the College of William and Mary and a collaboration of scientists from North America and France.The second area of research encompassed by this grant involvesstudies of fundamental properties of the neutron such as the electricand magnetic form factors, spin structure functions, higher-twisteffects, and tests of the fundamental Drell-Hearn-Gerassimov (GDH) Sum Rule. In these experiments, polarized electrons are scattered from an optically pumped, polarized Helium-3 gas target (which serves as a polarized neutron target), and are subsequently detected using twohigh resolution spectrometers. The first two of six approved experimentsusing polarized Helium-3 were successfully completed from August 1998-February 1999. These measurements provided high precision determinations of the GDH Sum Rule and magnetic form factor for the neutron at low momentum transfer where non-perturbative QCD effects are important. Data analysis from these first experiments, and polarized target improvements in preparation for the remaining experiments, are currently underway. Of particular interest is experiment E97-103 (Averett, Korsch et al) which will search for higher twist (non-perturbative QCD) contributions to the deep-inelastic structure function g2 for the neutron at low momentumtransfer. This will be accomplished by scattering longitudinallypolarized electrons from a transversely polarized Helium-3 target. It is expected that this experiment will achieve a statisticalerror which is approximately two orders of magnitude smaller than current world data and will provide much-needed quantitative guidancefor future theoretical calculations in this area.

托马斯·杰斐逊国家加速器设施(杰斐逊实验室)正在进行一个实验计划，用夸克自由度来研究核子的结构。这项研究将在两个不同的实验计划中进行。首先是所谓的‘G0’实验，它将利用宇称破坏电子散射来精确地确定质子的弱弹性形状因子。从这项测量中，我们可以提取出与核子内奇异夸克的电荷和电流分布直接相关的奇异电磁形状因子。为了实现高精度和宽广的运动覆盖范围的目标，正在建造一个专用的大接受度和液氢靶标。探测器的设计、原型研究和最终建造是弱电自旋物理组的共同责任(Finn等人)。这笔赠款涵盖的第二个研究领域涉及对中子基本性质的研究，如电和磁形状因子、自旋结构函数、高扭曲效应，以及基本Drell-Hain-Gerassimov(GDH)求和规则的测试。在这些实验中，极化的电子从光泵浦的极化的氦-3气体靶(作为极化的中子靶)散射，然后使用两个高分辨率光谱仪进行探测。1998年8月至1999年2月，六个已获批准的使用偏振氦-3的实验中的前两个实验成功完成。这些测量提供了低动量转移下中子的GDH求和规则和磁形状因子的高精度确定，在这种情况下非微扰QCD效应是重要的。这些第一批实验的数据分析以及为准备其余实验而进行的极化目标改进目前正在进行中。特别令人感兴趣的是实验E97-103(Averett，Korsch等人)，该实验将为低动量转移的中子寻找较高扭度(非微扰QCD)对深度非弹性结构函数G2的贡献。这将通过从横向极化的氦-3靶上散射纵向极化的电子来实现。预计本实验的统计误差将比目前的世界数据小约两个数量级，并将为今后这一领域的理论计算提供急需的定量指导。