The Outer Veto for the DarkSide-20k Dark Matter Search

天文证据表明，宇宙中27%的能量密度是由暗物质组成的——暗物质是一种无法用粒子物理标准模型描述的物质形式，只与已知粒子弱耦合。在天体物理学和宇宙学观测中，暗物质具有明显的引力效应。一个有希望的暗物质候选者是弱相互作用大质量粒子（WIMP），它是早期宇宙的遗迹，与原子内的核子有弱耦合。WIMP的光环预计会环绕整个星系，包括我们的太阳系。地球相对于它的运动产生了一种弱相互作用大质量粒子的通量，它们可能会散射到探测器的目标核上，从而产生核反冲。DarkSide-20k实验试图使用50吨活性体积的液态氩（LAr）作为“双相时间投影室（TPC）探测器”的一部分来探测此类wimp，该探测器能够完全抑制电磁背景。由于这些测量结果，液态氩探测器能够达到大的，几乎没有背景的暴露。然而，中子仍然是一个突出的背景：它们是在探测器材料中由宇宙射线μ子与探测器及其环境相互作用的罕见核反应中产生的。这些宇宙中子产生的能量很高，可以穿透探测器的屏蔽，可能在探测器中产生类似wimp的核反冲。由这笔拨款资助的工作将完成DarkSide-20k外否决的设计和实施，并确保探测器可以在没有宇宙起源中子背景的情况下运行。同时，这项工作将通过原型设计和安装工作为学生提供有价值的动手训练，让他们了解探测器设计和仪器仪表，以及与光电子、数据采集系统、模拟和分析工具相关的技能，从而为探测器设计提供信息。这项工作还将开发用于外展和算法开发的3D探测器可视化工具。该项目支持加州大学河滨分校的DarkSide-20k实验小组开展的工作，该小组负责设计和实施Outer Veto。这项工作将涉及外层否决权仪器的光学和机械模拟，以确保其稳定性，并满足消除宇宙起源中子背景所需的要求。基于模拟设计，将建立一个小型原型探测器，在将其部署到整个探测器之前，在校园测试光学和机械系统。此外，将测试能够覆盖具有低光敏传感器覆盖率的大面积探测器的具有成本效益的反射器，以确保它们在淹没在液态氩气中时保持其反射率。除了仪器之外，这笔赠款支持的工作还将为外部否决权设计和实施数据采集和低级数据处理系统。获得资助的工作还将完成LAr TPC净化系统吸气器的采购。由该实验资助的扩展项目将包括编程一个3D耳机来显示DarkSide-20k探测器的图像，并可视化其中发生的各种类型的信号。这个工具将被带到河滨地区的外展活动中，向社区成员和当地学校展示，它将为算法开发提供有用的工具，同时开发用于DarkSide-20k暗物质搜索的分析工具。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

An astronomical body of evidence indicates that 27% of the energy density of the universe is composed of dark matter — a form of matter that cannot be described by the Standard Model of particle physics and only weakly couples to the known particles. Dark Matter has clear gravitational effects evident in astrophysical and cosmological observations. A promising dark matter candidate is the Weakly Interacting Massive Particle (WIMP), a relic of the early universe with weak couplings to nucleons within atoms. A WIMP halo is expected to surround the entire galaxy including our solar system. The Earth’s motion relative to it creates a flux of WIMPs that may scatter on a target nucleus in the detector, creating a nuclear recoil. The DarkSide-20k experiment seeks to detect such WIMPs using a 50 tonne active volume of liquid argon (LAr) as part of a "dual-phase time projection chamber (TPC) detector", capable of completely suppressing electromagnetic backgrounds. As a result of these measurements, liquid argon detectors are capable of reaching large, nearly-background-free exposures. However, neutrons stand out as a remaining prominent background: they are produced in rare nuclear reactions in detector materials by cosmic-ray muons interacting with the detector and its environment. These cosmogenic neutrons are produced with high energies and can penetrate the detector shielding, potentially producing WIMP-like nuclear recoils in the detector. The work funded by this grant will finalize the design and carry out the implementation of the DarkSide-20k Outer Veto, and ensure the detector can operate free of cosmogenic neutron backgrounds. At the same time, this work will provide valuable hands-on training to students in detector design and instrumentation through prototyping and installation work, as well as in skills related to photoelectronics, data acquisition systems, and simulation and analysis tools needed to inform the detector design. The work will also develop 3D detector visualization tools for use in both outreach and in algorithm development.This project supports the work to be carried out by the University of California, Riverside group of the DarkSide-20k experiment, responsible for the design and implementation of the Outer Veto. This work will involve optical and mechanical simulations of the Outer Veto instrumentation to ensure its stability and that it meets the requirements needed to eliminate cosmogenic neutron backgrounds. Based on the simulation-informed design, a small-scale prototype detector will be built to test the optical and mechanical systems on campus before deploying them in the full detector. Additionally, cost-effective reflectors capable of covering large-area detectors with low photosensor coverage will be tested to ensure that they maintain their reflectance when submerged in liquid argon. In addition to the instrumentation, the work supported by this grant will carry out the design and implementation of the data acquisition and low-level data processing systems for the Outer Veto. The funded work will also complete the acquisition of the getter for the LAr TPC purification system. The outreach project funded by this experiment will involve programming a 3D headset to display an image of the DarkSide-20k detector and visualize various classes of signals occurring in it. This tool will be brought to outreach events around the Riverside area, shown to members of the community and at local schools, and it will provide a useful tool for algorithmic development while developing analysis tools for use in the DarkSide-20k dark matter search.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.