Searching for double beta decay with the LEGEND experiment

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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.