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

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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.