Polarized Electron Scattering from Nucleons

我们提出了一个极化电子散射实验方案，利用弱中性流和电磁探针来研究核子的味含量和自旋结构，并在标准模型之外进行新物理的探索。这些实验将主要在托马斯杰斐逊国家加速器实验室（Jefferson Lab）进行，一系列利用电子散射中宇称破缺的实验主要集中在确定奇异夸克对核子基态的贡献。这些实验包括测量在大厅A的宇称违反不对称性的前向角散射的质子，4-He，和208-Pb，在低动量转移。C厅的G 0实验将测量质子在前向和后向的宇称违反散射，以及一系列的动量转移，从而明确地绘制出核子的奇异夸克矢量形状因子作为四动量转移的函数。杰斐逊实验室最近批准了一项突破性的实验来测量质子的弱电荷。Qweak实验将通过精确测量低动量传递下的温伯格角并与高能实验的数据进行比较，提供弱混合角对能量标度依赖性的精确测试。这将提供一个超越标准模型的独特的敏感的物理探测器。因此，我们正在解决基础物理学中最重要的一个问题：标准模型如何以及在哪里崩溃？我们已经承担了Qweak实验的一个重要组成部分，区域III跟踪室，其建设最近由NSF重大研究仪器拨款资助。杰斐逊实验室的另一系列极化电子散射实验专注于使用极化3-He靶确定核子的自旋结构。GEN实验将首次测量大动量转移时的中子电形状因子。这是特别相关的考虑到最近有争议的结果theelectric形状因子的质子和新的理论工作的双光子交换机制。为了支持这一计划，研究有前途的新技术，涉及hyhybrid K-Rb细胞正在进行中的W M极化靶实验室。这一物理计划有一个大的教育组成部分; 11博士研究生正在工作组相关的活动，并支持要求从美国国家科学基金会为这些学生中的五个。每年我们平均指导七名本科生进行暑期或毕业论文研究。还要求NSF支持1.5个博士后职位。我们的团队靠近杰斐逊实验室，通过附属教师与杰斐逊实验室建立了牢固的联系，并且能够吸引优秀的威廉和玛丽本科生，确保了拟议研究的成功。

We propose a program of polarized electron scattering experiments, to use the weak neutralcurrent and electromagnetic probes to study the flavor content and spin structure of the nucleon,and to conduct a search for new physics beyond the Standard Model. The experiments will beconducted primarily at the Thomas Jefferson National Accelerator Facility (Jefferson Lab).A series of experiments using parity violation in electron scattering at Jefferson Lab arefocused on determining the elusive strange quark contribution to the nucleon ground state. Theseexperiments include measurements in Hall A of the parity-violating asymmetry in forward-anglescattering from the proton, 4-He, and 208-Pb, at low momentum transfer. The G0 experiment inHall C will measure parity-violating scattering from the proton at both forward and backwardangles, and for a range of momentum transfers, and thus will definitively map out the strangequark vector form factors for the nucleon as a function of four-momentum transfer.A groundbreaking experiment has recently been approved at Jefferson Laboratory tomeasure the weak charge of the proton. The Qweak experiment will provide a precision test ofthe energy scale dependence of the weak mixing angle by precisely measuring the Weinbergangle at low momentum transfer and comparing to data from high-energy experiments. This willprovide a uniquely sensitive probe of physics beyond the Standard Model. We are thusaddressing possibly the single most important question in fundamental physics: how and wheredoes the Standard Model break down? We have taken on an important component of the Qweakexperiment, the Region III tracking chambers, the construction of which has been recentlyfunded by an NSF Major Research Instrumentation grant.Another series of polarized electron scattering experiments at Jefferson Lab are focusedon determining the spin structure of the nucleon using polarized 3-He targets. The GENexperiment will make the first measurement on the neutron electric form factor at largemomentum transfers. This is particularly relevant given the recent controversial results for theelectric form factor of the proton and new theoretical work on two-photon exchangemechanisms. In support of this program, research into promising new technology involvinghybrid K-Rb cells is underway in the W&M polarized target lab.This physics program has a large educational component; eleven PhD graduate studentsare working on group-related activities, and support is requested from the NSF for five of thesestudents. Each year we supervise an average of seven undergraduates in summer or senior-thesisresearch. Support for 1.5 post-doctoral positions is also requested from the NSF. The proximityof our group to Jefferson Lab, its strong ties to Jefferson Lab through affiliated faculty, and itsability to attract excellent William and Mary undergraduate students, ensure the success of theproposed research.