Searching for double beta decay with the LEGEND experiment

传奇是一项旨在寻找无中微子双β衰变(0vbb)的实验，具有前所未有的灵敏度和发现潜力。对这一过程的观察将对粒子物理学产生最深远的影响。这是确定中微子的马约拉纳或狄拉克性质的唯一现实的方法，这可能有助于揭示宇宙中物质凌驾于反物质之上的机制。联想公司将使用一系列浓缩的高纯度锗(HPGe)探测器来搜索0vbb的Ge76同位素，该探测器工作在用作主动屏蔽的液态Ar中。联想将有两个阶段：联想-200，HPGe探测器容纳200公斤Ge76，联想-1000使用1000公斤浓缩的HPGe探测器。联想-200目前正在意大利格兰萨索地下实验室进行调试，物理数据将于今年晚些时候(2022年)开始采集。UCL集团是传奇的关键参与者，在模拟和数据分析、低本底技术和HPGe探测器开发方面做出了领先贡献。该项目将侧重于LEGOR-200的数据分析，重点是背景模型的建立和评估宇宙起源的Ar42的贡献，这是必须缓解的最具挑战性的背景之一，以达到最终的传奇敏感性。该项目还将包括一项旨在开发新型HPGe探测器和超低本底放射性分析方法的研发方案。

LEGEND is an experiment designed to search for neutrinoless double beta decay (0vbb) with an unprecedented sensitivity and discovery potential. The observation of this process will have the most profound implications for particle physics. It is the only realistic way to determine the Majorana or Dirac nature of the neutrino, which may shed light on the mechanism behind the dominance of matter over anti-matter in the universe. LEGEND will search for 0vbb of the Ge76 isotope using an array of enriched high purity germanium (HPGe) detectors operated in liquid argon that is used as an active shield. LEGEND will have two phases: LEGEND-200 with HPGe detectors hosting 200 kg of Ge76, and LEGEND-1000 employing 1000kg of enriched HPGe detectors. LEGEND-200 is currently undergoing commissioning at the Gran Sasso underground laboratory in Italy with physics data taking commencing later this year (2022). The UCL group is a key player in LEGEND providing leading contributions to simulations and data analysis, low background technologies and HPGe detector development. The project will focus on data analysis from LEGEND-200 with a focus on the background model building and assessing the contribution from cosmogenic Ar42, one of the most challenging backgrounds that must be mitigated to reach the ultimate LEGEND sensitivity. The project will also include an R&D programme aimed at developing novel HPGe detectors and ultra-low background radiopurity assay methods.