Collaborative Research: The DarkSide Dark-Matter Search Using Liquid Argon

大量的天文观测，包括星系旋转曲线、强引力透镜效应和宇宙微波背景的各向异性，表明已知物质只占观测到的宇宙质能的一小部分。剩余质量的有力候选者是具有不同于普通物质性质的弱相互作用的暗物质粒子。直接（非引力）探测暗物质将是一个变革性的发现，将代表科学史上的一个分水岭时刻，为研究黑暗宇宙打开了大门。该合同的目标是测试、现场安装、调试和过渡到DarkSide-20k （DS-20k）的运行，该实验能够将直接暗物质搜索的灵敏度提高到超过任何当前或目前资助的实验。该项目产生的更广泛的科学和技术影响包括：生产用于DS-20k和禁止核试验核查和放射性定年的低放射性地下氩气；继续研究在UAr勘探期间发现的地下气源，该气源提供了目前美国氦气消费量的15%；3Dπ是一种基于ar的TOF-PET系统，可以在降低辐射剂量的同时增强癌症筛查。暗物质的主要候选者是弱相互作用大质量粒子（WIMP），它是大爆炸的热遗迹，具有亚电弱尺度的自湮灭截面，质量在GeV/c2到TeV/c2之间。星系晕WIMP相对于地球上探测器的运动可能导致WIMP-核弹性碰撞，这种碰撞可以被低背景、低能量阈值探测器探测到，这种探测器能够明确地识别出在非常大的暴露过程中WIMP碰撞产生的少量核反冲。液态氩由于其优异的电离响应和独特的闪烁发光特性，可以为wimp -核碰撞提供出色的灵敏度和强大的背景抑制。参与该计划的美国国家科学基金会小组领导了DarkSide-20k液态氩暗物质搜索的概念和发展。在一项单独的中型合同的支持下，他们负责建造和交付最关键的DS-20k组件：液态氩时间投影室（LAr TPC），它是DS-20k暗物质探测器的核心，以及它的关键辅助组件，包括高压输送系统，以及相关的低温、净化和校准系统。在其他美国和国际资助机构（美国能源部、意大利国家核能研究所和加拿大创新基金会）的支持下，美国国家科学基金会小组也在领导采购所需的超低放射性氩气的活动，这种氩气是从科罗拉多州的一个特殊地下来源中提取的。该合同将支持美国团队对DS-20k探测器进行最终测试、现场安装、调试和过渡操作，并为科学分析做准备。darkde -20k实验将利用一个50吨填充（20吨基准）的两阶段时间投影室来扩展对暗物质的探索，在10年的运行中，达到4.9×10−48 cm2的横截面，90% c.l排除，1.6×10−47 cm2, 1 TeV/c2 WIMP的5 σ发现意义，远远超过任何当前或目前资助的实验。这将导致WIMP暗物质假说要么被发现，要么被证实，要么被排除，直至大气中微子的相干散射成为不可避免的背景。DarkSide-20k还将对来自银河系任何地方的星系超新星中微子爆发敏感。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。

A large body of astronomical observations, including galactic rotation curves, strong gravitational lensing, and the anisotropy of the cosmic microwave background, indicates that known matter only accounts for a small fraction of the observed mass-energy of the Universe. A strong candidate for the remaining mass is weakly interacting Dark Matter particles with properties different from ordinary matter. Direct (non-gravitational) detection of dark matter would be a transformational discovery and would represent a watershed moment in the history of science, opening the gates to the investigation of the dark universe. The goal of this award is the testing, on-site installation, commissioning, and transitioning to operations of DarkSide-20k (DS-20k), an experiment capable of pushing the sensitivity of direct dark matter searches beyond that of any current or presently funded experiment. Broader scientific and technological impacts from the project include, among others: the production of low-radioactivity underground argon (UAr) for DS-20k and for nuclear test ban verification and radiometric dating; the continued study of the underground gas source discovered during the UAr exploration, a source which supplies 15 % of the current U.S. helium consumption; and the continued development of 3Dπ, a LAr-based TOF-PET system that can enhance cancer screening while lowering radiation dose.A leading dark matter candidate is a weakly interacting massive particle, or WIMP, a thermal relic of the Big Bang that has a sub-electroweak-scale self-annihilation cross section and a mass in the GeV/c2 to TeV/c2 range. The motion of galactic halo WIMPs relative to a detector on Earth could result in WIMP-nucleus elastic collisions detectable by a low-background, low-energy-threshold detector capable of unambiguously identifying a small number of nuclear recoils from WIMP collisions over the course of a very large exposure. Thanks to its excellent ionization response and unique scintillation light emission characteristics, liquid argon can provide outstanding sensitivity for WIMP-nuclear collisions and strong background suppression. The U.S. NSF groups involved in this program have led the conception and development of the DarkSide-20k liquid argon dark matter search. With support from a separate Mid-scale award, they are responsible for the construction and delivery of the most critical DS-20k components: the liquid argon time projection chamber (LAr TPC) that serves as the heart of the DS-20k dark matter detector along with its critical ancillary components, including the high-voltage delivery system, and the associated cryogenic, purification, and calibration systems. The U.S. NSF groups are also leading the activities for the procurement of the required ultra-low radioactivity argon, which is extracted from a special underground source in Colorado, with support from other US and international funding agencies (U.S. Department of Energy, Istituto Nazionale di Fisica Nucleare of Italy, and Canada Foundation for Innovation). This award will support the U.S. groups for the final testing, on-site installation, commissioning, and transition to operations of the DS-20k detector and preparation for science analyses. The DarkSide-20k experiment will utilize a two-phase time projection chamber with a 50-tonne fill (20-tonne fiducial) to extend the exploration for dark matter, reaching, in a 10 years run, a cross section of 4.9×10−48 cm2 for a 90 % C.L. exclusion and 1.6×10−47 cm2 at a 5 σ discovery significance for a 1 TeV/c2 WIMP, well beyond any current or presently funded experiment. This will lead to either discovery, confirmation, or exclusion of the WIMP dark matter hypothesis down to the level where coherent scatters from atmospheric neutrinos become an unavoidable background. DarkSide-20k will also be sensitive to a galactic supernova neutrino burst originating anywhere in the Milky Way Galaxy.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.