Probing the Standard Model and Nuclear Structure with Parity-Violating Electron Scattering

该项目支持旨在回答有关物质的基本问题的研究。标准模型（我们目前对粒子和力如何相互作用的理解）没有描述的任何新物理学的本质是什么？这个问题将通过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）的两个大型合作实验中对质子和电子的弱电荷的精确测量来解决。质子和电子的弱电荷是这些粒子的普通电荷的弱力类似物。弱电荷在标准模型中得到了精确的预测。测量结果与这些预测的任何偏差都可能是尚未发现的大质量粒子的证据，这些粒子代表了超出我们目前理解的新物理学。该计划将支持研究生和本科生以及博士后，他们将成为该项目的重要组成部分。预期的活动包括一系列硬件和软件任务，这些任务将为这些人员提供良好的培训。基础研究方面的培训为基础研究以及更多应用研究和工业方面的职业发展提供了坚实的基础。本项目提供的资金将用于支持托马斯·杰斐逊国家加速器设施（TJNAF）的三个违反宇称的电子散射实验活动。Qweak实验将通过极低动量转移下违反宇称的电子散射来测量质子的中性弱电荷。质子的弱电荷在标准模型中有一个明确的预测；对它的精确测量对扩展标准模型的许多流行场景都很敏感。在此计划期间，该小组将主要为弱电荷结果的完整分析做出贡献，并完成从Qweak数据中提取物理结果的最后分析，用于其他两个主题-探测N到Delta跃迁中的强子奇偶性违反和测量Moller散射中的横向不对称性。MOLLER试验是一种被批准的TJNAF试验，用于升级的12 GeV TJNAF。它将通过精确测量极化电子在极低动量转移下对非极化电子的弹性散射中违反奇偶性的不对称性来测量电子的中性弱电荷。这将导致低能弱混合角的测定，其精度可与高能对撞机的最佳测定相媲美。它应该对标准模型之外的许多情景具有出色的敏感性。本课题期间，课题组将在束流电荷与位置监测器升级、光度监测器与背景探测器研制与建设、扫描探测器研制、仿真设计研究等方面为本实验做出重要贡献。在中子星结构和重离子碰撞中，富中子核的中子半径提供了一种重要的核结构测试方法。PREX-II和CREX实验预计将在此期间进行，并确定铅-208和钙-48中的中子半径。该小组将提供大角度散射监视器和线性测试设置，并将有助于分析波束监测和调制数据以及数据采集移位支持。

This project supports research that seeks to answer a fundamental question about matter. What is the nature of any new physics not described by the Standard Model - our current understanding of how particles and forces interact? This question will be addressed by precision measurements of the weak charges of the proton and electron at two large collaborative experiments at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) in Newport News, Virginia. The proton and electron's weak charges are the weak force analogs of the common electric charges of these particles. The weak charges are precisely predicted in the Standard Model. Any deviation of measurements from these predictions could be evidence of yet undiscovered massive particles that represent new physics beyond our current understanding. The program will support graduate and undergraduate students and a postdoctoral fellow, who will form an essential part of this project. The anticipated activities cover a range of hardware and software tasks that will provide excellent training for these individuals. This training in fundamental research provides a strong basis for careers both in basic research and in more applied research and industry. The funds provided by this project will support activities on three parity-violating electron scattering experiments at Thomas Jefferson National Accelerator Facility (TJNAF). The Qweak experiment will measure the proton's neutral weak charge via parity-violating electron scattering at very low momentum transfer. The proton's weak charge has a well-defined prediction in the Standard Model; a precise measurement of it is sensitive to many popular scenarios for extending the Standard Model. During the period of this program, the group will primarily be contributing to a complete analysis of the weak charge result as well as finalizing analyses to extract physics results from the Qweak data for two other topics - a probe of hadronic parity violation in the N to Delta transition and a measurement of the transverse asymmetry in Moller scattering. The MOLLER experiment is an approved TJNAF experiment intended for the upgraded 12 GeV TJNAF. It will measure the electron's neutral weak charge by making a precision measurement of the parity-violating asymmetry in the elastic scattering of polarized electrons on unpolarized electrons at a very low momentum transfer. This will result in a determination of the weak mixing angle at low energy with a precision comparable to the best determinations from high-energy colliders. It should have excellent sensitivity to many beyond the Standard Model scenarios. During the period of this project, the group will make important contributions to this experiment by working on beam charge and position monitor upgrades, luminosity monitor and background detector development and construction, scanner detector development, and simulation design studies. Neutron radii in neutron-rich nuclear provide an important test of nuclear structure with applications to neutron star structure and heavy ion collisions. The PREX-II and CREX experiments are anticipated to run in this period and determine the neutron radii in lead-208 and calcium-48. The group will provide large angle scattering monitors and a setup for linearity testing and will contribute to the analysis of beam monitoring and modulation data and data-taking shift support.