Precision Measurements of Parity Violation

这笔赠款支持研究测量质子的弱电荷，然后使用这种测量来研究基本物质和相互作用标准模型的新方面。标准模型以优雅的方式描述了自然界四种力中的三种：电磁相互作用、弱相互作用和强相互作用。质子的弱电荷象它的电荷和质量一样是一个基本性质，它决定了质子对弱相互作用的响应。它还与弱相互作用和电磁相互作用如何相互混合有关。由于标准模型对混合如何随相互作用中交换的动量变化做出了很好的预测，只有一套非常精确的测量存在于非常高的动量转移值，因此在低动量转移值下精确测量质子的弱电荷是对标准模型的严格测试。此外，它对尚未包括在标准模型中的物理很敏感。JLab的量子弱实验将通过散射质子中的极化电子并测量它们的散射速率来进行这种精确的测量。从这种散射中提取质子的弱电荷将需要用专门的设备进行精细的校准。由这笔赠款支持的研究小组正在开发一种探测器，它将触发校准阶段的所有其他探测器，并集成校准阶段的所有组件。这个项目将解决硬件和软件问题，因此学生和博士后研究人员将获得广泛的有价值的技能。

This grant supports research to measure the weak charge of the proton and then use thatmeasurement to investigate new aspects of the Standard Model of fundamental matter andinteractions. The Standard Model describes three of the four forces of nature in an elegantmanner; those three forces are the electromagnetic interaction, the weak interaction, andthe strong interaction. The weak charge of the proton is a basic property, like its electriccharge and mass, which determines the proton's response to the weak interaction. It is alsorelated to how the weak and electromagnetic interactions mix with each other. Becausethe Standard Model makes well dened predictions of how that mixing varies with theamount of momentum that is exchanged in an interaction, with only one set of very precisemeasurements existing at very high values of momentum transfer, a precise measurementof the proton's weak charge at a low value of momentum transfer is a rigorous test of theStandard Model. Additionally, it is sensitive to physics not yet included in the StandardModel.The Qweak experiment at JLab will carry out this precise measurement by scatteringpolarized electrons from protons and measuring the rate at which they scatter. Extractingthe weak charge of the proton from this scattering will require delicate calibrations withspecialized equipment. The research group supported by this grant is developing a detectorthat will trigger all the other detectors of the calibration phase, as well as integrating allcomponents of the calibration phase. Both hardware and software issues will be addressed inthis project so the students and postdoctoral researchers will gain a wide range of valuableskills.