Nucleon Spin Structure Studies Using Parity Violating and Inelastic Electron Scattering

在托马斯杰斐逊国家加速器设施（杰斐逊实验室），一项研究核子结构的实验计划正在进行中。 这项研究将在两个不同的实验项目中进行。 第一个是所谓的“G 0”实验，它将使用宇称破坏电子散射来精确确定质子的弱弹性形状因子。 从这个测量中，人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。 为了实现该实验的高精度和广泛的运动学覆盖的目标，正在建造专用的大接受度和液氢靶。 探测器的设计、原型研究和最终建造是电弱自旋物理组（Finn等人）的共同责任。第二个研究领域包括中子的基本性质的研究，如电磁形状因子、自旋结构函数、高扭转效应，以及基本的Drell-Hearn-Gerassimov（GDH）求和规则的检验。 在这些实验中，极化电子从光泵，极化氦-3气体目标（作为极化中子目标）散射，并随后使用两个高分辨率光谱仪检测。 1998年8月至1999年2月，六个批准的使用极化氦-3的实验中的前两个成功完成。 这些测量提供了高精度的GDH求和规则和磁形状因子的中子在低动量转移的非微扰QCD效应是重要的。 这些第一次实验的数据分析，以及为其余实验做准备的极化目标改进，目前正在进行中。 特别令人感兴趣的是实验E97-103（Averett，Korsch等人），该实验将寻找更高的扭曲（非微扰QCD）对中子在低动量转移时的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靶散射横向极化的电子来实现。 预计该实验将获得比当前世界数据小约两个数量级的几何误差，并将为该领域未来的理论计算提供急需的定量指导。

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.