Germanium-Based Neutrinoless Double-Beta Decay Searches

中微子是亚原子粒子，在宇宙中既丰富又难以捉摸。它们是电中性的，几乎不与物质相互作用。此外，中微子的质量很小，其原因尚不清楚，可能与中微子是否是自己的反粒子有关。中微子的粒子-反粒子性质可以通过寻找一种极其罕见的放射性衰变形式来研究，即无中微子双β衰变。最常见的放射性形式之一是（正常）β衰变，其中一个电子与反中微子沿着从原子核中发射出来。当一个核子发射出两个电子和两个反中微子时，就会发生双中微子双β。最后，一个更奇特的衰变过程被假设为无中微子双β衰变;在这个过程中，发射出两个电子而没有反中微子，这只有在中微子是它们自己的反粒子时才可能。寻找这种假设的衰变是核科学的优先事项，积极的观察将揭示为什么宇宙中的物质比反物质多的令人信服的奥秘。该项目促进了正在进行的和未来的锗-76中无中微子双β衰变的实验研究。该项目将推进实验核物理，产生新的科学知识，并帮助早期职业科学家发展他们的技术技能。该项目的主要研究活动集中在南达科他州的MAJORANA DEMONSTRATOR（MJD）实验和多阶段大型浓缩锗无中微子双β衰变实验（LEGEND）。该项目支持MAJORANA的持续运行以及对完整物理数据集的数据分析，特别是通过有助于能量校准和统计分析，从而实现演示器的最终双β衰变灵敏度。MAJORANA校准数据中关于（α，中子）反应的新科学知识将来自拟议的去激发伽马射线测量。LEGEND项目旨在测量10 e28年以上的双β衰变半衰期。最初的LEGEND-200阶段正在建设中，后来的LEGEND-1000阶段正在设计中。USD对LEGEND的研究活动包括：1）为LEGEND-200阶段的广泛模拟工作做出贡献，2）通过调查不断发展的基线设计和有前途的替代设计的宇宙成因和放射成因背景，扩大LEGEND-1000背景预测和建模的现有工作，以及3）开发将显著抑制LEGEND背景的分析例程。该项目将用于培养本科生，研究生和博士后学生在精密核物理技术和大型复杂数据集的分析。 PI还将通过参加南达科他州Lead的Sanford Underground Research Facility（SURF）的“中微子日”活动参与物理教育和外展活动。该奖项反映了NSF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 are subatomic particles which are both abundant in the Universe and elusive at the same time. They are electrically neutral and barely interact with matter. In addition, neutrinos have tiny masses and the reason for this is unknown and could be related to whether neutrinos are their own antiparticles. The particle-antiparticle nature of neutrinos can be investigated by searching for an extremely rare form of radioactive decay, namely neutrinoless double beta decay. One of the most common forms of radioactivity is (normal) beta decay, where one electron is emitted from a nucleus along with an antineutrino. Two-neutrino double beta occurs when two electrons and two antineutrinos are emitted by a neucleus. Finally, a more exotic decay process has been hypothesized called neutrinoless double beta decay; in this process two electrons and no antineutrinos are emitted, and this is only possible if neutrinos are their own antiparticles. The search for this hypothetical decay is a priority for nuclear science, and a positive observation would shed light on the compelling mystery of why there is more matter than antimatter in the Universe. This project facilitates ongoing and future experimental searches for neutrinoless double beta decay in Germanium-76. This project will advance experimental nuclear physics, yield new scientific knowledge, and help early-career scientists develop their technical skills. The major research activities of this project focus on the MAJORANA DEMONSTRATOR (MJD) experiment in South Dakota and the multi-phased Large Enriched Germanium Experiment for Neutrinoless double beta Decay (LEGEND). This project supports MAJORANA’s continued operation as well as its data analysis of the full physics dataset, particularly by contributing to energy calibration and statistical analysis, so that the final double beta decay sensitivity of the DEMONSTRATOR can be realized. New scientific knowledge on (alpha, neutron) reactions in the MAJORANA calibration data will come from the proposed measurement of deexcitation gamma rays. The LEGEND project aims to measure a double beta decay half-life beyond 10e28 yr. The initial LEGEND-200 phase is under construction and the later LEGEND-1000 phase is under design. Research activities at USD for LEGEND include 1) contributing to the extensive simulation efforts of the LEGEND-200 phase, 2) expanding existing efforts on LEGEND-1000 background prediction and modeling by investigating cosmogenic and radiogenic backgrounds for both the evolving baseline design and promising alternative designs, and 3) developing analysis routines that will significantly suppress LEGEND backgrounds.The project will serve to train undergraduate, graduate and postdoctoral students in the techniques of precision nuclear physics and in the analysis of large and complex data sets. The PI will also engage in physics education and outreach through his participation in "Neutrino Day" at the Sanford Underground Research Facility (SURF) in Lead, South Dakota.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.