2025/05/15 by Acharya, H., Ackermann, N., Agostini, M. +256 · 14 citations
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #Nuclear Experiment (nucl-ex)
paper · doi:10.48550/arxiv.2505.10440
The LEGEND collaboration is searching for neutrinoless double beta (0νββ) decay by operating high-purity germanium detectors enriched in 76Ge in a low-background liquid argon environment. Building on key technological innovations from GERDA and the MAJORANA DEMONSTRATOR, LEGEND-200 has performed a first 0νββ 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 0.5+0.3-0.2 cts/(keV kg yr) in the 0νββ 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 2.8 × 1026 yr on the half-life of 0νββ decay, reveals no evidence for a signal and sets a new observed lower limit at T0ν1/2 > 1.9 × 1026 yr (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 mββ < 75-200 meV, depending on the adopted nuclear matrix element.