The Majorana Collaboration concluded operation of its Demonstrator array of enriched Ge-76 detectors on March 3, 2021. This array has been operating since June 2015 at the Sanford Underground Research Facility in South Dakota to search for neutrinoless double-beta decay in 30 kg of Ge-76. During this time, the Majorana Demonstrator has collected valuable low-background data and set competitive half-life limits for the decay. In addition, the collaboration is making use of this unique detector to search for other rare events and set limits on new physics beyond the standard model. The operation of the Majorana Demonstrator served as R&D and helped pave the way for the next-generation experiment called LEGEND.
While the primary operational phase is complete, Majorana’s analysis program will continue. The half-life limits published to date correspond to about 40% of the collected exposure. An upcoming data release will report on an improved half-life limit for neutrinoless double-beta decay using data collected through 2019, at which point the experiment paused for a hardware upgrade. For this upgrade, five of the Majorana detectors were removed to be tested in the GERDA liquid argon cryostat in preparation for their deployment in LEGEND-200. In their place, four of the larger inverted-coax point-contact Ge detectors in production for LEGEND were deployed in the Demonstrator vacuum cryostat to study their performance in its well-characterized, low-noise environment. The Majorana collaboration is studying these new detectors and will include their contribution in the final background analysis and half-life limit.
Later this month, the Majorana Demonstrator will be opened so that the enriched Ge-76 detectors can be removed and shipped to LNGS in Italy where they will be deployed in LEGEND-200, along with the detectors from the GERDA experiment and other new detectors. The Majorana Ge detectors of natural isotopic abundance will remain and, after a reconfiguration, will be redeployed in the Majorana Demonstrator cryostat and shield for continued operation. With more natural detector data, the Majorana background model can be refined and physics searches that do not rely on the enriched Ge-76 can continue.
