First Results on the Search for Lepton Number Violating Neutrinoless Double-β Decay with the LEGEND-200 Experiment

AbstraktAbstract

The LEGEND Collaboration is searching for neutrinoless double-beta ((Formula presented)) decay by operating high-purity germanium detectors enriched in (Formula presented) in a low-background liquid argon environment. Building on key technological innovations from the GERmanium Detector Array (GERDA) experiment and the MAJORANA DEMONSTRATOR experiment, LEGEND-200 has performed a first (Formula presented) decay search based on 61.0 kg yr of data. Over half of this exposure comes from our highest performing detectors, including newly developed inverted-coaxial detectors, and is characterized by an estimated background level of (Formula presented) in the (Formula presented) decay signal region. A combined analysis of data from GERDA, the MAJORANA DEMONSTRATOR, and LEGEND-200, characterized by a 90% confidence level exclusion sensitivity of (Formula presented) on the half-life of (Formula presented) decay, reveals no evidence for a signal and sets a new observed lower limit at (Formula presented) (90% confidence level). Assuming the decay is mediated by Majorana neutrinos, this corresponds to an upper limit on the effective Majorana mass in the range (Formula presented), depending on the adopted nuclear matrix element.

The LEGEND Collaboration is searching for neutrinoless double-beta ((Formula presented)) decay by operating high-purity germanium detectors enriched in (Formula presented) in a low-background liquid argon environment. Building on key technological innovations from the GERmanium Detector Array (GERDA) experiment and the MAJORANA DEMONSTRATOR experiment, LEGEND-200 has performed a first (Formula presented) decay search based on 61.0 kg yr of data. Over half of this exposure comes from our highest performing detectors, including newly developed inverted-coaxial detectors, and is characterized by an estimated background level of (Formula presented) in the (Formula presented) decay signal region. A combined analysis of data from GERDA, the MAJORANA DEMONSTRATOR, and LEGEND-200, characterized by a 90% confidence level exclusion sensitivity of (Formula presented) on the half-life of (Formula presented) decay, reveals no evidence for a signal and sets a new observed lower limit at (Formula presented) (90% confidence level). Assuming the decay is mediated by Majorana neutrinos, this corresponds to an upper limit on the effective Majorana mass in the range (Formula presented), depending on the adopted nuclear matrix element.