LEGEND-200 Commissioning, Operations and an Investigation of HPGe Detector Performance

Despite being discovered over 70 years ago, much remains unknown about the neutrino, such as its mass and its quantum nature. It is the only fermion in the standard model with mass but no electric charge making it the only potential candidate to be a Majorana particle, or a particle that is its own antiparticle. To determine the Majorana nature of the neutrino one can observe a theorized decay process called neutrinoless double beta decay (0νββ) where a nucleus beta decays twice simultaneously but does not emit any neutrinos. The Large Enriched Germanium Experiment for Neutrinoless double beta Decay (LEGEND) collaboration has deployed its first array, LEGEND-200, of high purity germanium (HPGe) detectors enriched in the double beta decaying isotope 76Ge to search for 0νββ. This dissertation describes the construction of the HPGe detector units and their installation into the LEGEND-200 array. The operation of the array including the parameters used to acquire data and the calibration of the HPGe detectors will be discussed. An analysis of the operational performance of the HPGe detectors during its first physics measurement period will demonstrate the feasibility of the novel ICPC detector design for LEGEND-1000 while exploring several problems exhibited by a subset of detectors. Sources of some of these problems will be identified as well as some solutions and necessary studies that need to be performed going forward. Finally, results from LEGEND-200’s first physics measurement will be summarized.