DOE OSTI ¡ 3683764
First Results on the Search for Lepton Number Violating Neutrinoless Double-đ˝ Decay with the LEGEND-200 Experiment
Abstract
The LEGEND Collaboration is searching for neutrinoless double-beta (0â˘đâ˘đ˝â˘đ˝) decay by operating high-purity germanium detectors enriched in 76 Ge 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 0â˘đâ˘đ˝â˘đ˝ 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$^{+0.3}_{â0.2}$ â˘cts/(keV ton yr) in the 0â˘đâ˘đ˝â˘đ˝ 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 Ă10 26 yr on the half-life of 0â˘đâ˘đ˝â˘đ˝ decay, reveals no evidence for a signal and sets a new observed lower limit at đ$^{â˘0đ}_{1/2}$ > 1.9 Ă 10 26 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 đ đ˝â˘đ˝ < 75â200 meV, depending on the adopted nuclear matrix element.
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Acharya, H. [University of North Carolina; Triangle Universities Nuclear Laboratory] (ORCID:0009000022198511), Ackermann, N. [Max-Planck-Institut fĂźr Kernphysik], Agostini, M. [University College London] (ORCID:0000000311515301), Alexander, A. [University College London] (ORCID:0000000156081397), Andreoiu, C. [Simon Fraser University] (ORCID:0000000201962792), Araujo, G. R. [University of ZĂźrich] (ORCID:0000000344560774), Avignone, F. T. [University of South Carolina; Oak Ridge National Laboratory], Babicz, M. [University of ZĂźrich] (ORCID:0000000210175440), Bae, W. [University of Texas at Austin] (ORCID:0000000276467577), Bakalyarov, A. M. [National Research Centre âKurchatov Instituteâ], Balata, M. [Laboratori Nazionali del Gran Sasso] (ORCID:0000000167456983), Barabash, A. S. [National Research Centre âKurchatov Instituteâ] (ORCID:0000000251300922), Barbeau, P. S. [Duke University; Triangle Universities Nuclear Laboratory] (ORCID:0000000288918988), Barton, C. J. 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[UniversitĂ degli Studi di Milano Bicocca; Istituto Nazionale di Fisica Nucleare] (ORCID:000000018734206X), Capra, S. [Istituto Nazionale di Fisica Nucleare; UniversitĂ degli Studi di Milano] (ORCID:0000000233304145), Carminati, M. [Politecnico di Milano; Istituto Nazionale di Fisica Nucleare] (ORCID:0000000234854317), Carney, R. M. D. [Lawrence Berkeley National Laboratory; Lawrence Berkeley National Laboratory] (ORCID:0000000156594440), Cattadori, C. [Istituto Nazionale di Fisica Nucleare] (ORCID:0000000178856253), Cesarano, R. [Gran Sasso Science Institute; Laboratori Nazionali del Gran Sasso] (ORCID:0009000395081471), Chan, Y.-D. [Lawrence Berkeley National Laboratory] (ORCID:0009000374747326), Chapman, J. R. [University of North Carolina; Triangle Universities Nuclear Laboratory] (ORCID:0009000498152981), Chernogorov, A. [National Research Centre âKurchatov Instituteâ] (ORCID:0000000337212165), Chiu, P.-J. [University of ZĂźrich] (ORCID:0000000237720090), Christofferson, C. D. [South Dakota Mines] (ORCID:0009000518429352), Clark, M. L. [University of North Carolina; Triangle Universities Nuclear Laboratory] (ORCID:0000000237408291), Colon-Rivera, A. I. [Duke University; Triangle Universities Nuclear Laboratory] (ORCID:0009000506564688), Comellato, T. [Technical University of Munich] (ORCID:0000000337805139), DâAndrea, V. [Istituto Nazionale di Fisica Nucleare] (ORCID:0000000320374133), Deckert, R. [Technical University of Munich] (ORCID:000900060431341X), Detwiler, J. A. [University of Washington] (ORCID:0000000290504610), Di Giacinto, A. [Laboratori Nazionali del Gran Sasso], Di Marco, N. [Gran Sasso Science Institute; Laboratori Nazionali del Gran Sasso] (ORCID:0000000317237613), Dixon, T. [University College London] (ORCID:0000000187876336), Dong, K.-M. [University of South Dakota] (ORCID:0000000199459388), Drobizhev, A. [Lawrence Berkeley National Laboratory] (ORCID:0009000472623028), Duran, G. 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[University of North Carolina; Triangle Universities Nuclear Laboratory] (ORCID:0009000737501107), Gold, M. [University of New Mexico] (ORCID:0000000273003160), Gooch, C. [Max-Planck-Institut fĂźr Physik] (ORCID:0009000165965749), GrĂźnauer, G. [University TĂźbingen], Green, M. P. [North Carolina State University; Triangle Universities Nuclear Laboratory; Oak Ridge National Laboratory] (ORCID:0000000219588030), Gruszko, J. [University of North Carolina; Triangle Universities Nuclear Laboratory] (ORCID:0000000237772237), Guinn, I. [Oak Ridge National Laboratory] (ORCID:0000000224243272), Guiseppe, V. E. [Oak Ridge National Laboratory] (ORCID:0000000200787101), Gurentsov, V. [Institute for Nuclear Research of the Russian Academy of Sciences] (ORCID:0009000076668435), Gurov, Y. [Joint Institute for Nuclear Research] (ORCID:0000000286954555), Gusev, K. [Technical University of Munich; Joint Institute for Nuclear Research] (ORCID:0000000204950551), Hackett, B. [Oak Ridge National Laboratory; Max-Planck-Institut fĂźr Physik] (ORCID:0000000249092861), Hagemann, F. [Max-Planck-Institut fĂźr Physik] (ORCID:0000000150213328), Haranczyk, M. [Laboratori Nazionali del Gran Sasso; Jagiellonian University] (ORCID:0000000238414108), Henkes, F. [Technical University of Munich; Max-Planck-Institut fĂźr Kernphysik] (ORCID:0009000546256479), Henning, R. [University of North Carolina; Triangle Universities Nuclear Laboratory] (ORCID:0000000186512960), Herrera, J. [North Carolina State University; Triangle Universities Nuclear Laboratory] (ORCID:0009000606322395), Hervas Aguilar, D. [Technical University of Munich] (ORCID:0000000296860659), Hinton, J. [Max-Planck-Institut fĂźr Kernphysik] (ORCID:0000000210317760), HodĂĄk, R. [Czech Technical University in Prague], Hoffmann, H. F. R. [Technische Universität Dresden] (ORCID:0009000431886569), Howe, M. A. [University of North Carolina; Triangle Universities Nuclear Laboratory] (ORCID:0009000909239185), Huber, M. [Technical University of Munich] (ORCID:0009000052122999), Hult, M. [Joint Research Centre] (ORCID:0000000292486786), Ianni, A. [Laboratori Nazionali del Gran Sasso] (ORCID:0000000269623682). 2026-01-16. First Results on the Search for Lepton Number Violating Neutrinoless Double-đ˝ Decay with the LEGEND-200 Experiment. https://doi.org/10.1103/25tk-nctn
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