DarkSide

天文观测提供了强有力的证据，表明已知物质只占观测到的宇宙总质量-能量的一小部分。一个主要的暗物质候选者是所谓的弱相互作用大质量粒子（WIMP），一种被预测为大爆炸遗留下来的粒子。对暗物质的直接（非引力）探测将是一项革命性的发现，对科学具有广泛的根本性重要性，开启了对黑暗宇宙的新研究。这种对暗物质的首次测量可能是通过低背景、低能量阈值探测器探测到的WIMP-核碰撞来实现的，这种探测器能够在长时间的暴露期内从WIMP碰撞中区分出少量的核反冲。液态氩已被确定具有独特的发光特性，在提供强背景抑制的同时，为此类WIMP碰撞提供了出色的灵敏度。该奖项为下一代WIMP暗物质实验——DarkSide-20k的建造提供了支持。DarkSide国际合作率先使用高放射性液态氩来寻找罕见的WIMP相互作用。DarkSide-20k探测器的设计基准暴露量约为20kT低本底液态氩，将在格兰萨索国家实验室的地下深实验室中运行。美国国家科学基金会DarkSide团队通过该奖项得到支持，建造中央暗物质探测器液态氩时间投影室，包括相关的高压输送、低温、净化和校准系统。授予的活动涉及可转让的技术，其中包括：为实验以及禁止核试验核查和放射性测年生产低放射性地下氩气；地下气源研究；低背景、大面积、单光子低温硅光电倍增管光电传感器的研制用于增强癌症筛查的液态氩基飞行时间正电子发射断层扫描系统；世界上最高的低温蒸馏塔，以提高医疗和能源应用中稳定稀有同位素的可用性。还包括培训和教育机会，包括在科尔特斯-杜兰戈地区的暑期学校经历，这将为STEM中代表性不足的群体提供更多机会。美国暗面计划领导了暗面50实验计划，证明了在液态氩气中进行无背景搜索的可行性。DarkSide-20k实验将把WIMP暗物质搜索在横截面与质量范围内的灵敏度扩展到4.6e-48 cm-平方，以达到90%的置信限排除，对于1 TeV/c-平方的WIMP质量，在500t-年的暴露后，发现意义将达到1.5e-47 cm-平方。独特的美国专业知识在建设贵重液体探测器是杠杆，以确保这下一代探测器的成功。该项目的规模及其由此产生的灵敏度超过了目前运行的探测器，导致WIMP暗物质假说的发现、确认或排除，使大气中微子的相干散射成为不可约的背景。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。

Astronomical observations have provided strong evidence that the known matter accounts for only a small fraction of the observed total mass-energy of the Universe. A leading dark matter candidate is the so-called weakly interacting massive particle, or WIMP, a predicted relic particle of the Big Bang. Direct (non-gravitational) detection of dark matter would be a transformational discovery of fundamental importance broadly to the sciences, opening new investigations of the dark universe. Such first measurements of dark matter may be possible via WIMP-nucleus collisions detectable at low-background, low-energy threshold detectors capable of distinguishing a small number of nuclear recoils from WIMP collisions over a long exposure period. Liquid argon has been identified to have unique light emission properties that provide excellent sensitivity for such WIMP collisions while providing strong background suppression. This award provides support for the fabrication of a next-generation WIMP dark matter experiment, DarkSide-20k. The DarkSide international collaboration has pioneered the use of liquid argon with high radiopurity to search for rare WIMP interactions. The DarkSide-20k detector, with a designed fiducial exposure volume of approximately 20kT of low-background liquid argon, will operate in the INFN Laboratori Nazionali del Gran Sasso deep underground lab. The US NSF DarkSide team is supported via this award to build the central dark matter detector liquid argon time-projection chamber, including the associated high-voltage delivery, cryogenic, purification and calibration systems. The awarded activities involve transferable technologies that include: the production of low-radioactivity underground argon for the experiment as well as for nuclear test ban verification and radiometric dating; studies of underground gas sources; development of low-background, large-area, single-photon cryogenic silicon photomultiplier photosensors; liquid argon-based time-of-flight positron emission tomography system for enhanced cancer screening, and; the world’s tallest cryogenic distillation tower to improve availability of stable rare isotopes for medical and energy applications. Also included are training and education opportunities, including a summer school experience in the Cortez-Durango region that will offer increased access to underrepresented groups in STEM.The US DarkSide program led the DarkSide-50 experimental program that demonstrated the viability of background-free searches in liquid argon. The DarkSide-20k experiment will extend the sensitivity of WIMP dark matter searches in the cross-section vs. mass range to 4.6e-48 cm-squared for the 90% confidence limit exclusion, and to 1.5e-47 cm-squared 5 sigma discovery significance for a 1 TeV/c-squared WIMP mass after a 500t-yr exposure. Unique US expertise in the construction of noble liquid detectors is leveraged to ensure the success of this next generation detector. The scale of project, and its resultant sensitivity, exceeds that of detectors currently operating, leading to discovery, confirmation, or exclusion of the WIMP dark matter hypothesis to the level where coherent scatters from atmospheric neutrinos become an irreducible background.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.