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

大量天文证据表明，宇宙能量密度的27%由暗物质组成，暗物质是一种物质形式，不能用粒子物理的标准模型来描述，而且只能与已知粒子弱耦合。暗物质具有明显的引力效应，这在天体物理和宇宙学观测中是显而易见的。一个有希望的候选暗物质是弱相互作用大质量粒子(WIMP)，它是早期宇宙的遗迹，与原子内的核子弱耦合。WIMP光晕预计将环绕整个银河系，包括我们的太阳系。地球相对于它的运动产生了WIMP流量，该流量可能会散射到探测器中的目标核上，从而产生核反冲。Darkside-20K实验试图使用50吨有效体积的液态Ar(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。作为这些测量的结果，液态Ar探测器能够达到大的、几乎没有背景的曝光。然而，中子仍然是一个突出的背景：它们是在探测器材料中罕见的核反应中由宇宙射线µ子与探测器及其环境相互作用产生的。这些宇宙产生的中子能量很高，可以穿透探测器的屏蔽，有可能在探测器中产生类似WIMP的核反冲。这项由这笔赠款资助的工作将最终完成设计并实施Darkside-20k外层否决权，并确保探测器可以在没有宇宙产生的中子背景的情况下运行。同时，这项工作将通过原型和安装工作，为学生提供探测器设计和仪器方面的宝贵实践培训，以及与光电子学、数据采集系统以及为探测器设计提供信息所需的模拟和分析工具有关的技能。这项工作还将开发3D探测器可视化工具，用于外展和算法开发。该项目支持加州大学河滨分校黑暗-20k实验小组开展的工作，负责设计和实施外部否决权。这项工作将涉及对外层否决权仪器进行光学和机械模拟，以确保其稳定性，并确保其满足消除宇宙产生的中子背景所需的要求。在模拟设计的基础上，将建造一个小型原型探测器，在将光学和机械系统部署到完整探测器之前，在校园内对它们进行测试。此外，将对能够覆盖大面积低光电传感器覆盖范围的反射器进行测试，以确保它们在浸入液态Ar中时保持其反射率。除仪器外，这笔赠款支持的工作还将设计和实施外层否决权的数据采集和低级数据处理系统。资助的工作还将完成Lar TPC净化系统吸气剂的采购。由这项实验资助的推广项目将涉及对3D耳机进行编程，以显示Darkside-20k探测器的图像，并将其中出现的各种信号可视化。该工具将被带到河滨地区周围的外展活动中，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NSF的法定使命，并通过使用基金会的智力优势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.