Collaborative Research: DarkSide-20K: A Global Program for the Direct Detection of Dark Matter Using Low-Radioactivity Argon

多次天文观测已经确定，宇宙中大约85%的物质不是由正常的原子组成的，而是由不发射或吸收光的未被探测到的基本“暗物质”粒子组成的。破译这种所谓的暗物质的本质对宇宙学、天体物理学和高能粒子物理学至关重要。一个主要的假设是，它是由大爆炸后瞬间产生的弱相互作用大质量粒子（wimp）组成的。如果wimp是暗物质，那么它们在我们星系中的存在可以通过位于地下深处的探测器的原子核散射来检测，以帮助排除宇宙射线造成的背景。直接探测WIMP暗物质将解决粒子物理学和宇宙学中的一个基本谜团，为了解宇宙的主要物质组成和粒子物理学标准模型之外的物理学提供一个独特的窗口。该奖项是为了支持nsf资助的DarkSide （DS）小组建造和运行DarkSide-20k (DS-20k)，这是一个使用有效（基准）质量为23吨（20吨）的液态氩时间投影室（LAr TPC）直接搜索WIMP的项目。LAr TPC在很大程度上依赖于从地下来源获得的氩气（UAr）的利用。计划中的Aria UAr净化项目可能会提高全球有价值的稳定稀有同位素（如O-18、N-15和C-13）的可用性，这些同位素用于各种医疗、工业和能源生产应用。生产数百吨低放射性铀用于DS-20k和其他技术用途，需要检测禁止核试验核查所需的Ar-37，以及用于放射性测年的Ar-39。特别的E&amp；O项目计划重点教育K-12教师关于基础物理及其与暗物质探测的关系，为高中和本科生重新启动暑期学校体验，以及为参与少数民族服务机构的本科生提供研究机会。DS-20k是建立在暗黑面-50 （DS-50）的成功基础上的，暗黑面-50自2013年以来在LNGS运行，使用大气氩气（AAr）和地下氩气（UAr）填充产生了两个零背景科学结果。DS-50在UAr中显示出39Ar减少1400。电子反冲（ER）背景在目标区域被完全抑制，在1.5 × 10^7范围内的分辨率优于1分之一。这些结果证明了大型LAr tpc在“仪器无背景模式”下工作的能力，在这种模式下，在DS-20k计划暴露的感兴趣区域，预计不到0.1个事件（除了大气和漫射超新星背景中微子的弹性散射产生的实际核反冲）。DS-20k将具有超低背景，能够就地测量其背景，对质量为1 TeV/c2 （10 TeV/c2）的wimp -核子截面的灵敏度为1.2 x 10^-47 cm2 (1.1 x 10^-46 cm2)，在5年的运行期间，暴露量为100 t /年。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。

Multiple astronomical observations have established that about 85% of the matter in the universe is not made of normal atoms, but must be otherwise undetected elementary "dark matter" particles that do not emit or absorb light. Deciphering the nature of this so-called Dark Matter is of fundamental importance to cosmology, astrophysics, and high-energy particle physics. A leading hypothesis is that it is comprised of Weakly Interacting Massive Particles, or WIMPs, that were produced moments after the Big Bang. If WIMPs are the dark matter, then their presence in our galaxy may be detectable via scattering from atomic nuclei in detectors located deep underground to help reject backgrounds due to cosmic rays. Direct detection of WIMP dark matter would solve a fundamental mystery in particle physics and cosmology, providing a unique window to learning about the primary matter constituent of the Universe and of physics beyond the Standard Model of particle physics. This award is to support the NSF-funded DarkSide (DS) groups for the construction and operation of DarkSide-20k (DS-20k), a direct WIMP search using a Liquid Argon Time Projection Chamber (LAr TPC) with an active (fiducial) mass of 23 tons (20 tons).The LAr TPC relies heavily on the utilization of argon obtained from underground sources, or UAr. The planned Aria project for UAr purification may improve the worldwide availability of valuable stable rare isotopes such as O-18, N-15, and C-13, used for various medical, industrial and energy generation applications. The production of hundreds of tonnes of low-radioactivity UAr for DS-20k and for other technical uses requiring detection of Ar-37 for nuclear test ban verification, and Ar-39, for radiometric dating. Special E&O programs are planned with focus on educating K-12 teachers about basic physics and how it relates to dark matter detection, re-starting a summer school experience for high-school and undergraduate students, as well giving research opportunities to undergraduate students at participating underrepresented-minority serving institutions.DS-20k builds on the success of DarkSide-50 (DS-50), operating at LNGS since 2013, which produced two zero-background science results using atmospheric argon (AAr) and then underground argon (UAr) fills. DS-50 demonstrated an 39Ar reduction of 1400 in the UAr. Electron recoil (ER) background was shown to be completely suppressed in the region of interest, with discrimination better than 1 part in 1.5 x 10^7. These results demonstrated the ability of large LAr TPCs to operate in an "instrumental background-free mode" - a mode in which less than 0.1 events (other than actual nuclear recoils from elastic scattering of atmospheric and diffuse supernova background neutrinos) are expected in the region of interest for the planned exposure of DS-20k. DS-20k will have ultra-low backgrounds, with the ability to measure its backgrounds in situ, and sensitivity to WIMP-nucleon cross sections of 1.2 x 10^-47 cm2 (1.1 x 10^-46 cm2) for WIMPs of 1 TeV/c2 (10 TeV/c2) mass, to be achieved during a 5 yr run with exposure of 100 t yr.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.