MRI Consortium: Collaborative Research: Development of the Phase-I DarkLight Experiment at Jefferson Laboratory

粒子物理学是发现物质和能量的基本成分的科学，涉及从最小到最大尺度的宇宙探索。20世纪粒子物理学的一个显著成就是标准模型的发展，它令人印象深刻地描述了广泛的基本粒子，如夸克和轻子，以及它们之间的相互作用（力）。但是标准模型是不完整的，我们知道在它之外还有重要的物理学。证据是什么？例如，天文观测表明，标准模型的已知粒子只占宇宙总物质的1/6。剩下的被称为“暗物质”，因为我们不能直接看到它。为了寻找暗物质，许多实验正在进行中或正在计划阶段，暗物质可能是一种粒子，也可能是多种粒子，或者完全是其他的东西。这个核磁共振奖将允许来自DarkLight联盟机构的年轻物理学家在加速器科学，探测器和目标的开发和利用，测量和分析，以及寻找超越标准模型的新物理的新证据方面进行优秀的培训。该主要研究仪器奖授予麻省理工学院、汉普顿大学、亚利桑那州立大学和天普大学组成的一个联盟，用于在托马斯·杰斐逊国家实验室开发、建造和运行暗光实验的第一阶段。该计划解决了最近发布的粒子物理项目优先小组报告（称为P5）的两个科学驱动因素：暗物质和寻找新粒子和相互作用。暗光实验将利用杰斐逊实验室现有的能量回收直线加速器（ERL）的1兆瓦电子束，以100 MeV的速度入射到一个无窗的氢气目标上，寻找电子和正电子对的证据，这些电子和正电子对可能是质量区域10到90 MeV的大质量暗光子a´的衰变产物。正如天体物理学观测所表明的那样，这样的A´将轻子（如电子和正电子）耦合到暗物质上，并且可以解释μ子异常磁矩（所谓的“g-2异常”）的观测值与标准模型的可能差异。DarkLight具有在排他反应中搜索A´的独特功能。DarkLight仪器第一阶段的实现将有三个科学目标：开展涉及能量回收直线光束与DarkLight气体靶和螺线管相互作用的重要加速器科学研究；仔细测量标准模型背景过程；并利用这一新的实验技术，通过检测质量区域30 ~ 70 MeV/c2的e+e-对，对a´进行首次搜索。

Particle Physics is the science of discovery of the fundamental constituents of matter and energy and is involved in the exploration of the Universe from the smallest to the largest scales. A remarkable achievement of Twentieth Century Particle Physics was the development of the Standard Model that describes impressively well a broad spectrum of fundamental particles such as quarks and leptons and the interactions (the forces) among them. But the Standard Model is incomplete and we know there is important physics that lies beyond it. What is the evidence? As an example, astronomical observations indicate that the known particles of the Standard Model make up only 1/6 of the total matter in the Universe. The remainder is called "Dark Matter" because we don't see it directly. A number of experiments are underway or in the planning stage to look for the Dark Matter, which might be one type of particle or possibly many or perhaps something else entirely. This MRI award will allow the excellent training of young physicists from the institutions in the DarkLight consortium in accelerator science, detector and target development and utilization, measurement and analysis, and search for new evidence of new physics beyond the Standard Model.This Major Research Instrumentation award is made to a consortium of MIT, Hampton University, Arizona State University and Temple University to develop, build and operate a first phase of the DarkLight experiment at Thomas Jefferson National Laboratory. This program addresses two of the science drivers of the recently released Report of the Particle Physics Project Prioritization Panel (called P5): Dark Matter and the Search for New Particles and Interactions. The DarkLight experiment will utilize the 1 Megawatt electron beam of the existing energy-recovering linac (ERL) at Jefferson Lab, incident at 100 MeV on a windowless hydrogen gas target, to search for evidence of electron and positron pairs which could be decay products of a massive Dark Photon called the A´ in the mass region 10 to 90 MeV. Such an A´ couples leptons (such as electrons and positrons) to dark matter, as suggested by astrophysical observations, and may explain a possible discrepancy with the Standard Model in the observed value of the anomalous magnetic moment of the muon (the so called "g-2 anomaly"). DarkLight has the unique feature of searching for the A´ in exclusive reactions. The phase-I realization of the DarkLight instrument will have three scientific goals: to carry out important accelerator science studies involving the interaction of the energy-recovering linac beam with the DarkLight gas target and solenoid; to carefully measure Standard Model background processes; and to carry out a first search for the A´ via detection of e+e- pairs in the mass region 30 to 70 MeV/c2 using this new experimental technique.