Search for the Neutrinoless Double Beta Decay with the LEGEND Experiment

用 LEGEND 实验寻找无中微子双贝塔衰变

• 批准号: 2312278
• 负责人: Karol Lang
• 金额: $ 63.5万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-07-15 至 2026-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2312278&HistoricalAwards=false
• 关键词: Search; Neutrinoless; Double; Beta; Decay

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.

中微子是不带电荷的基本粒子，长期以来被认为质量为零，弥漫在宇宙中。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非常弱。已经确定了三种类型的中微子，推测它们彼此独立。然而，1998年在这些类型之间的中微子振荡的一项了不起的发现证明了中微子有质量。这一发现比以往任何时候都更推动了对中微子性质的进一步研究。揭开中微子的本质对于更好地理解基本粒子及其基本相互作用具有深远的影响。一些自然猜想表明，对中微子的更深入了解可能会让我们一窥早期宇宙中存在的极高能量的现象，可能会拓宽我们对基本相互作用的知识，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。该奖项支持派和他的团队进行实验中微子物理研究，并参与传奇实验，该实验旨在寻找一种极其罕见的核转变--无中微子双β衰变。这项传奇实验不仅将增进我们对自然界中一些最稀有现象的了解，还将开发一种独特的低本底计数技术，这种技术可能会应用于物理学之外，并对社会产生普遍好处。应用可能包括测量环境中的人为辐射或超灵敏的放射性检测。这些活动教育和培训年轻的研究人员，建立一个最先进的科学项目。传奇实验将使用从浓缩的Ge-76中生长出来的高纯度锗晶体。届时将有大约300个总质量为1吨的探测器。在五年的暴露中，实验将达到大约10^{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自然和宇宙来源的放射性。联想采用了一个多层的实验装置，由一个水箱组成，水箱里有一个低温杜瓦尔，里面既有地下开采的、在Ar-39中被耗尽的Ar，也有环绕晶体的大气液态Ar。探测器串将进一步由集光纤维或薄板主动屏蔽，以标记和抑制晶体附近的本底放射性。为了达到实验目标，所有探测器部件都必须具有超高的放射性纯度和超低的氡射率。该实验目前正在通过收集约200公斤晶体的数据并使用之前开发的装置来测试关键策略。这一初步阶段将为目前正在设计的新的、更优化的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，包括使用放射性纯塑料来探测锗晶体周围的液态Ar中的发光事件。实现这些目标需要与该组织长期合作的行业合作伙伴的参与。这一奖项反映了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。