Precision Measurement of the Parity-Violating Asymmetryin e-2H Deep Inelastic Scattering

该项目将使用托马斯·杰斐逊国家加速器设施(JLab)上的6GeV电子束测量电子-氘深度非弹性散射(PV-DIS)中的宇称破坏不对称性。自然界的宇称对称性是电磁和强相互作用的一个基本性质，但在1957年被发现在弱相互作用中被破坏。从那时起，宇称破坏现象被广泛用于研究电弱相互作用的标准模型和核子结构。然而，到目前为止，大多数破坏宇称的散射实验都是在弹性散射区域进行的，在弹性散射区域，核子作为刚体进行反应。深度非弹性散射的一个显著特征是，在这种情况下，核子分解为其基本成分--夸克和胶子--因此可以揭示弱电相互作用或核子结构的不同方面。更具体地说，我们的目标是提取耦合系数C2q，它测量电子与Z0玻色子之间的电弱相互作用强度和夸克与Z0玻色子之间的电弱相互作用强度的乘积，并将其精度提高到目前公布的值的8倍。这一结果将为目前弱电标准模型之外可能出现的新物理提供新的启示，并对其他中低能标准模型实验具有补充作用。在不久的将来，在JLab升级后，PVDIS的测量将得到扩展，并将探索一系列关于电弱物理和核子结构的主题，包括通过直接观察夸克水平上的电荷对称性破坏而可能的新发现。PI作为发言人在这个项目中发挥着主导作用。她正在领导构建实验所需的新数据采集系统的努力。此次硬件开发将为暑期本科生和研究生提供宝贵的培训和研究经验。这项实验将成为至少一名弗吉尼亚大学研究生的博士项目。从长远来看，6GeV的测量为PI发展更大规模(可能是国际)的合作奠定了基础，以在12GeV能源升级的JLab开展这一计划的扩展。

This project will measure the parity-violating asymmetry in electron-deuterium deep inelastic scattering (PV-DIS) using the 6 GeV electron beam at the Thomas Jefferson National Accelerator Facility (JLab). The parity symmetry of nature is a fundamental property of the electromagnetic and strong interactions but was found to be violated in weak interactions in 1957. Since then, the phenomenon of parity violation has been widely used to study both the Standard Model of electro-weak interactions and the nucleon structure. Most parity violating scattering experiments so far, however, were carried out in the elastic scattering regime where the nucleon reacts as a rigid body. A remarkable feature of deep inelastic scattering is that in this regime the nucleon breaks down to its fundamental constituents -- quarks and gluons -- thus different aspects of electroweak interaction or nucleon structure can be revealed. More specifically, our goal is to extract the coupling coefficients C2q, which measures the product of the strengths of the electro-weak interactions between an electron and the Z0 boson and that between a quark and the Z0, and improve its precision to eight times better than the current published value. Such result would shed light on possible new physics beyond the current electroweak Standard Model and is complementary to other low and medium-energy Standard Model test experiments. In the near future, the PVDIS measurement will be extended after the JLab upgrade and a broad range of topics on electro-weak physics and the nucleon structure, including a potential new discovery by directly observing the charge-symmetry violation at the quark level, will be explored.The PI is playing a leading role in this project as a spokesperson. She is leading the effort to construct a new data acquisition system required for the experiment. This hardware development will provide valuable training and research experience for summer undergraduate and graduate students. This experiment will become the Ph.D. project for at least one graduate student from UVa. In the long term, the 6 GeV measurement forms the basis for the PI to develop a larger-scale (possibly international) collaboration to carry out extension of this program at the 12 GeV energy upgraded JLab.