Search for the Neutrinoless Double Beta Decay with the LEGEND Experiment

中微子是一种基本粒子，不带电荷，长期以来被认为质量为零，它遍布宇宙。众所周知，它们很难被探测到，因为它们与任何其他已知的基本粒子的相互作用都极其微弱。已经确定了三种类型的中微子，大概是相互独立的。然而，1998年对这两种类型之间的中微子振荡的一项重大发现表明，中微子具有质量。这一发现比以往任何时候都更激发了对中微子性质的进一步研究。揭示中微子的本质对更好地理解基本粒子及其基本相互作用具有深远的意义。一些自然的猜想表明，对中微子的深入了解可能会让我们对早期宇宙中存在的极高能量现象有所了解，可能会拓宽我们对基本相互作用的认识，可能会揭示物质对反物质的主导地位，并有助于更好地理解宇宙的早期演化。该奖项支持PI和他的团队在实验中微子物理方面进行研究，并参与LEGEND实验，该实验旨在寻找极其罕见的核跃迁-中微子双β衰变。LEGEND实验不仅将提高我们对自然界中一些最罕见现象的认识，而且还将发展出一种独特的低背景计数技术，这种技术可能应用于物理学之外，对社会有普遍的好处。应用可包括环境中人为辐射的测量或超灵敏的放射性检测。这些活动教育和训练年轻的研究人员建立一个最先进的科学项目。LEGEND实验将使用从富集的锗76中生长出来的高纯度锗晶体。将有大约300个总质量为一吨的探测器。在五年的暴露中，实验将达到大约10^ b{28}年的半衰期灵敏度。为了实现这一目标，必须消除许多可能模仿信号的天然和宇宙产生的放射性来源。LEGEND采用了多层实验装置，该装置由一个水箱组成，水箱中装有低温杜瓦瓶，其中既有地下开采的氩（在氩-39中耗尽），也有围绕晶体的大气液态氩。探测器串将进一步被光收集纤维或薄板主动屏蔽，以标记和抑制晶体附近的背景放射性。为达到实验目的，探测器各组成部分必须具有超高的放射性纯度和超低的氡辐射。该实验目前正在通过收集约200公斤晶体的数据和使用先前开发的装置来测试关键策略。这个初步阶段将为目前正在设计的新的和更好的优化探测器配置扫清道路。PI和他的团队将与机构合作，模拟和构建各种配置的原型，其中涉及放射性纯塑料，用于检测锗晶体周围液态氩气中的发光事件。实现这些目标需要与集团长期合作的工业伙伴进行接触。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。

Neutrinos, elementary particles that have no charge and were long believed to have zero mass, permeate the universe. They are notoriously difficult to detect, as they interact extremely weakly with any other known elementary particles. Three types of neutrino have been identified, presumably independent of each other. Yet a remarkable discovery of neutrino oscillations between these types in 1998 demonstrated that neutrinos have mass. This discovery motivated further investigations of properties of neutrinos more than ever before. Unraveling the nature of neutrinos can have far-reaching implications for better understanding of elementary particles and their fundamental interactions. Some natural conjectures suggest that deeper understanding of neutrinos may provide a glimpse onto phenomena at extremely high energies that existed in the early Universe, could broaden our knowledge of the fundamental interactions, may shed light onto the dominance of matter over antimatter, and can help to better understand the early evolution of the Universe. This award supports the PI and his group in conducting research in experimental neutrino physics and participating in the LEGEND experiment, which is designed to search for an extremely rare nuclear transition - neutrinoless double beta decay. The LEGEND Experiment will not only advance our knowledge about some of the rarest phenomena in Nature but it will also develop a unique low background counting technique that may be applied outside of physics and be of general benefit to society. Applications may include measurements of anthropogenic radiation in the environment or ultra-sensitive detection of radioactivity. These activities educate and train young researchers in building a state-of-the-art science project.The LEGEND Experiment will employ high-purity germanium crystals grown out of enriched germanium-76. There will be about 300 detectors of a total mass of one ton. In a five-year exposure the experiment will reach the half-life sensitivity of about 10^{28} years. To achieve this goal many sources of natural and cosmogenic radioactivity that may mimic a signal must be eliminated. LEGEND has adopted a multi-layered experimental setup composed of a water tank that houses a cryogenic dewar with both underground-mined argon, which is depleted in argon-39, and atmospheric liquid argon surrounding the crystals. Detector strings will be further actively shielded by light-collecting fibers or thin plates to tag and suppress background radioactivity in the vicinity of the crystals. Ultra-high radio-purity and ultra-low radon emanation of all detector components are necessary to reach experimental objectives. The experiment is currently testing critical strategies by collecting data with about 200 kg of crystals and using a setup developed previously. This preliminary phase will clear a way for the new and better optimized detector configuration currently being designed. The PI and his team will collaborate with institutions to simulate and construct prototypes of various configurations involving radio-pure plastics for detecting light-yielding events in liquid argon around germanium crystals. Achieving the objectives requires engaging industrial partners with which the group has had a long-standing cooperation.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.