Qweak: Weak Charge of the Proton and New Physics at Jefferson Laboratory (JLab E02-020, E05-008)

Qweak：杰斐逊实验室的质子弱电荷和新物理（JLab E02-020、E05-008）

• 批准号: 261721-2013
• 负责人: Page, Shelley
• 金额: $ 14.57万
• 依托单位: University of Manitoba
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2013
• 资助国家: 加拿大
• 起止时间: 2013-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=525347
• 关键词: Qweak; Weak; Charge; Proton; New

A search for physics beyond the Standard Model of fundamental particle interactions has been underway for the past decade at Jefferson Laboratory in Newport News, VA. The 'Qweak' experiment will measure the proton's weak charge -- a fundamental property that determines how a proton responds to the weak interaction. One of the Standard Model's key predictions is that the strengths of all interactions, characterized by 'coupling constants', are in fact energy scale - dependent. This property has not yet been tested to high precision for the weak interaction. By measuring the proton's weak charge, we will be able to determine whether the anticipated 'running' of the weak interaction with energy scale is in fact borne out by experiment. If it is not, some new physics processes must be taking place, which would have profound implications for our understanding of the fundamental interactions of matter. The key to our experimental test is to isolate the weak interaction contribution to electron-proton scattering by comparing the scattering rates when the electron beam is polarized in two mirror-image states, referred to as parity-violation. This means that we compare the scattering rate when the electron beam spins are aligned parallel and antiparallel to their direction of motion, incident on a liquid hydrogen (proton) target. The expected dependence on the electron spin direction is very small - only 0.2 parts per million, and we are measuring this tiny asymmetry to within +/- 4% of its value in order to test the predictions of the Standard Model theory. After 7 years of development, the Qweak experiment took data almost full time at Jefferson Laboratory's continuous electron beam accelerator facility for 2 years, beginning in mid-2010. A substantial data set has been acquired, from which the weak charge of the proton will be determined. We made use of Jefferson Lab's excellent quality polarized electron beam to help ensure that systematic errors would be very small, in order to carry out these very precise measurements. Our group has played a key role in the Qweak experiment since it was first conceived in 2001; our contributions, with NSERC support, have been and will continue to be pivotal in ensuring the success of this challenging effort.

在过去的十年里，弗吉尼亚州纽波特纽斯的杰斐逊实验室一直在寻找超越基本粒子相互作用标准模型的物理学。“Qweak”实验将测量质子的弱电荷——这是决定质子如何对弱相互作用做出反应的基本性质。标准模型的关键预测之一是，所有相互作用的强度，以“耦合常数”为特征，实际上依赖于能量尺度。这一性质尚未对弱相互作用进行高精度测试。通过测量质子的弱电荷，我们将能够确定预期的弱相互作用在能量尺度上的“运行”是否实际上得到了实验的证实。如果不是这样，那么一定会发生一些新的物理过程，这将对我们对物质基本相互作用的理解产生深远的影响。我们实验测试的关键是通过比较电子束在两种镜像状态下极化时的散射率来隔离弱相互作用对电子-质子散射的贡献，称为宇称破坏。这意味着我们比较了当电子束自旋与运动方向平行和反平行时，入射到液氢（质子）目标上的散射率。预期的对电子自旋方向的依赖非常小——只有百万分之0.2，为了检验标准模型理论的预测，我们正在测量这种微小的不对称性，误差在其值的±4%以内。经过7年的发展，Qweak实验从2010年中期开始，在杰斐逊实验室的连续电子束加速器设备上进行了2年的数据采集。已经获得了大量的数据集，从中可以确定质子的弱电荷。为了进行这些非常精确的测量，我们利用杰斐逊实验室的优质极化电子束来帮助确保系统误差非常小。自2001年Qweak实验首次提出以来，我们的团队在该实验中发挥了关键作用；在NSERC的支持下，我们的贡献已经并将继续在确保这一具有挑战性的努力取得成功方面发挥关键作用。