Open Access

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

H. Acharya ^1,2, N. Ackermann³, M. Agostini ⁴, A. Alexander ⁴, C. Andreoiu ⁵, G. R. Araujo ⁶, F. T. Avignone, III^7,8, M. Babicz ⁶, W. Bae ⁹ et al. (LEGEND Collaboration^¶)

W. Bae ⁹, A. M. Bakalyarov¹⁰, M. Balata ¹¹, A. S. Barabash ¹⁰, P. S. Barbeau ^12,2, C. J. Barton ¹⁴, L. Baudis ⁶, C. Bauer³, E. Bernieri ^13,14, L. Bezrukov ¹⁵, K. H. Bhimani ^1,2, V. Biancacci ^16,11, E. Blalock ^17,2, S. J. Borden ¹⁸, G. Borghi ^19,20, F. Borra ^13,14, B. Bos ^1,2, A. Boston ²¹, V. Bothe ³, R. Bouabid ^12,2, R. Brugnera ^22,23, N. Burlac ¹¹, M. Busch ^12,2, S. Calgaro ^6,23, L. Canonica ^25,26, S. Capra ^20,27, M. Carminati ^19,20, R. M. D. Carney ^28,29, C. Cattadori ²⁶, R. Cesarano ^16,11, Y.-D. Chan ²⁹, J. R. Chapman ^1,2, A. Chernogorov ¹⁰, P.-J. Chiu ^6,*, C. D. Christofferson ³⁰, M. L. Clark ^1,2, A. I. Colon-Rivera ^12,2, T. Comellato ³¹, V. D’Andrea ¹⁴, R. Deckert ³¹, J. A. Detwiler ¹⁸, A. Di Giacinto¹¹, N. Di Marco ^16,11, T. Dixon ⁴, K.-M. Dong ³², A. Drobizhev ²⁹, G. Duran ^1,2, Yu. Efremenko ^33,8, S. R. Elliott ³⁴, C. H. J. Emmanuel ^1,2, E. Engelhardt ^1,2, E. Esch ³⁵, M. T. Febbraro ^8,†, F. Ferella ¹¹, D. E. Fields ³⁶, C. Fiorini ^19,20, M. Fomina ³⁷, N. Fuad ³⁹, R. Gala ^17,2, A. Galindo-Uribarri ⁸, A. Gangapshev ¹⁵, A. Garfagnini ^22,23, S. Gazzana ⁴⁰, A. Geraci ^19,20, L. Gessler ³⁵, C. Ghiano ¹¹, A. Gieb ^31,3, S. Giri ^1,2, M. Gold ³⁶, C. Gooch ²⁴, G. Grünauer³⁵, M. P. Green ^17,2,8, J. Gruszko ^1,2, I. Guinn ⁸, V. E. Guiseppe ⁸, V. Gurentsov ¹⁵, Y. Gurov ³⁷, K. Gusev ^31,37, B. Hackett ^8,24, F. Hagemann ²⁴, M. Haranczyk ^11,41, F. Henkes ^31,3, R. Henning ^1,2, J. Herrera ^17,2, D. Hervas Aguilar ³¹, J. Hinton ³, R. Hodák⁴², H. F. R. Hoffmann ⁴³, M. A. Howe ^1,2, M. Huber ³¹, M. Hult ⁴⁴, A. Ianni ¹¹, K. Jędrzejczak⁴¹, J. Jochum ³⁵, R. W. L. Jones ³⁸, D. S. Judson ²¹, M. Junker ¹¹, J. Kaizer ⁴⁵, V. Kazalov ¹⁵, M. F. Kidd ⁴⁶, T. Kihm ³, K. Kilgus ³⁵, A. Klimenko ³⁷, K. T. Knöpfle³, I. Kochanek ¹¹, O. Kochetov³⁷, I. Kontul ⁴⁵, L. L. Kormos ³⁸, V. N. Kornoukhov ⁴⁷, P. Krause ³¹, H. Krishnamoorthy ⁸, V. V. Kuzminov ¹⁵, K. Lang ⁹, M. Laubenstein ¹¹, N. N. P. N. Lay ³¹, E. León^1,2,‡, A. Leder ³⁴, B. Lehnert ⁴³, A. Leonhardt ³¹, N. Levashko ¹⁰, L. Y. Li ⁴, A. Li ^48,49, Y.-R. Lin ¹⁸, M. Lindner³, I. Lippi ²³, A. Love³⁰, A. Lubashevskiy ³⁷, B. Lubsandorzhiev ¹⁵, N. Lusardi ^19,20, C. Macolino^51,11, B. Majorovits ²⁴, F. Mamedov ⁴², L. Manzanillas ²⁴, G. G. Marshall ⁴, R. D. Martin ⁵⁰, E. L. Martin ^12,2, R. Massarczyk ³⁴, A. Mazumdar ^1,2,34, G. McDowell ³⁶, D.-M. Mei ³², S. P. Meireles ^51,11, M. Menzel ³⁵, S. Mertens ^31,3, E. Miller ¹⁸, I. Mirza ³³, M. Misiaszek ⁴¹, M. Morella ^11,16, B. Morgan ⁵², T. Mroz ^41,§, D. Muenstermann³⁸, C. J. Nave ¹⁸, I. Nemchenok ³⁷, M. Neuberger ³¹, N. O’Briant^1,2, F. Paissan ¹⁴, L. Papp ³¹, L. S. Paudel ³², K. Pelczar ⁴⁴, L. Pertoldi ^31,23, W. Pettus ³⁹, F. Piastra ⁶, M. Pichotta ⁴³, P. Piseri ^27,20, A. W. P. Poon ²⁹, P. P. Povinec ⁴⁵, M. Pruckner ³¹, A. Pullia ^27,20, W. S. Quinn ⁴, D. C. Radford ⁸, Y. A. Ramachers ⁵², A. Razeto ¹¹, M. Redchuk ²³, A. L. Reine ³⁹, S. Riboldi ^27,20, K. Rielage ³⁴, C. Romo-Luque ³⁴, N. Rossi ¹¹, S. Rozov ³⁷, T. J. Ruland ⁸, N. Rumyantseva ^31,37, J. Runge ^12,2, R. Saakyan ⁴, S. Sailer ³, G. Salamanna ^13,14, F. Salamida^51,11, G. Saleh ^6,22,23, V. Sandukovsky³⁷, C. Savarese ¹⁸, S. Schönert³¹, A.-K. Schütz²⁹, D. C. Schaper ^39,34, L. Schlüter²⁹, S. J. Schleich ³⁹, O. Schulz ²⁴, M. Schwarz ³¹, B. Schwingenheuer ³, C. Seibt ⁴³, O. Selivanenko ¹⁵, G. Senatore ⁶, A. Serafini ^22,23, K. Shakhov ³⁷, E. Shevchik ³⁷, M. Shirchenko ³⁷, Y. Shitov ⁴², H. Simgen³, F. Šimkovic⁴², S. Simonaitis-Boyd ⁴⁹, M. Skorokhvatov ¹⁰, M. Slavíčková⁴², A. Smolnikov ^37,††, J. A. Solomon^1,2, G. Song ¹⁸, A. C. Sousa³⁰, A. R. Sreekala ⁶, L. Steinhart ³⁵, I. Štekl⁴², T. Sterr ³⁵, M. Stommel ⁵³, S. A. Sullivan ³, R. R. Sumathi ⁵⁴, K. Szczepaniec ¹¹, L. Taffarello ²³, D. Tagnani ¹⁴, D. J. Tedeschi ⁷, T. N. Thorpe ³⁴, V. Tretyak ³⁷, M. Turqueti ²⁸, E. E. Van Nieuwenhuizen ^12,2, L. J. Varriano ¹⁸, S. Vasilyev ³⁷, A. Veresnikova ¹⁵, C. Vignoli ¹¹, C. Vogl ³¹, K. von Sturm ^22,23, A. Warren ³², D. Waters ⁴, S. L. Watkins ^34,∥, C. Wiesinger ^31,3, J. F. Wilkerson ^1,2,8, M. Willers ^31,3, C. Wiseman ¹⁸, M. Wojcik ⁴¹, D. Xu ⁴, W. Xu ³², E. Yakushev ³⁷, T. Ye ⁵⁰, C.-H. Yu ⁸, V. Yumatov ¹⁰, D. Zinatulina ³⁷, K. Zuber ⁴³, and G. Zuzel ⁴¹ (LEGEND Collaboration^¶)

¹Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599, USA
²Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA
³Max-Planck-Institut für Kernphysik, Heidelberg 69117, Germany
⁴Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom
⁵Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
⁶Physik-Institut, University of Zürich, Zürich 8057, Switzerland
⁷Department of Physics and Astronomy, University of South Carolina, Columbia, South Carolina 29208, USA
⁸Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
⁹Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA
¹⁰National Research Centre “Kurchatov Institute”, Moscow 123098, Russia7
¹¹Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Gran Sasso, 67100 Assergi (AQ), Italy
¹²Department of Physics, Duke University, Durham, North Carolina 27708, USA
¹³Università degli Studi di Roma Tre, Rome 00146, Italy
¹⁴Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tre, Rome 00146, Italy
¹⁵Institute for Nuclear Research of the Russian Academy of Sciences, Moscow 119991, Russia
¹⁶Gran Sasso Science Institute, L’Aquila 67100, Italy
¹⁷Department of Physics, North Carolina State University, Raleigh, North Carolina 27607, USA
¹⁸Center for Experimental Nuclear Physics and Astrophysics, and Department of Physics, University of Washington, Seattle, Washington 98195, USA
¹⁹Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria, Milan 20133, Italy
²⁰Istituto Nazionale di Fisica Nucleare, Sezione di Milano, Milan 20133, Italy
²¹University of Liverpool, Liverpool L69 3BX, United Kingdom
²²Dipartimento di Fisica e Astronomia dell’Università degli Studi di Padova, Padua 35131, Italy
²³Istituto Nazionale di Fisica Nucleare, Sezione di Padova, Padua 35131, Italy
²⁴Max-Planck-Institut für Physik, Garching b. München 85748, Germany
²⁵Università degli Studi di Milano Bicocca, Milan 20126, Italy
²⁶Istituto Nazionale di Fisica Nucleare, Sezione di Milano Bicocca, Milan 20126, Italy
²⁷Università degli Studi di Milano, Milan 20133, Italy
²⁸Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
²⁹Institute for Nuclear and Particle Astrophysics and Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
³⁰South Dakota Mines, Rapid City, South Dakota 57701, USA
³¹Department of Physics, TUM School of Natural Sciences, Technical University of Munich, 85748 Garching b. München, Germany
³²Department of Physics, University of South Dakota, Vermillion, South Dakota 57069, USA
³³Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37916, USA
³⁴Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
³⁵University Tübingen, Tübingen 72076, Germany
³⁶Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131, USA
³⁷Joint Institute for Nuclear Research, Dubna 141980, Russia
³⁸Department of Physics, Lancaster University, Lancaster LA1 4YW, United Kingdom
³⁹Center for Exploration of Energy and Matter, and Department of Physics, Indiana University, Bloomington, Indiana 47405, USA
⁴⁰Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, 00044 Frascati (RM), Italy
⁴¹M. Smoluchowski Institute of Physics, Jagiellonian University, Cracow 30-348, Poland
⁴²Czech Technical University in Prague, Institute of Experimental and Applied Physics, CZ-11000 Prague, Czech Republic
⁴³Technische Universität Dresden, Dresden 01069, Germany
⁴⁴European Commission, Joint Research Centre, Directorate for Nuclear Safety and Security, Geel 2440, Belgium
⁴⁵Department of Nuclear Physics and Biophysics, Comenius University, Bratislava SK-84248, Slovakia
⁴⁶Tennessee Tech University, Cookeville, Tennessee 38505, USA
⁴⁷National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409 Moscow, Russia
⁴⁸Department of Physics, University of California, San Diego, La Jolla, California 92093, USA
⁴⁹Hal𝚤c𝚤oğlu Data Science Institute, University of California, San Diego, La Jolla, California 92093, USA
⁵⁰Department of Physics, Engineering Physics & Astronomy, Queen’s University, Kingston, Ontario K7L 3N6, Canada
⁵¹Dipartimento di Scienze Fisiche e Chimiche dell’Università degli Studi dell’Aquila, L’Aquila 67100, Italy
⁵²Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
⁵³Leibniz-Institut für Polymerforschung Dresden e.V., Dresden D-01069, Germany
⁵⁴Leibniz-Institut für Kristallzüchtung, Berlin D-12489, Germany

^*Present address: Department of Physics, National Taiwan University, Taipei 10617, Taiwan.
^†Present address: Air Force Institute of Technology, Dayton, Ohio 45433, USA.
^‡Present address: 111 Huntington Ave 14th floor, Boston, Massachusetts 02199, USA.
^§Present address: The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences, Kraków, Poland.
^∥Present address: Pacific Northwest National Laboratory, Richland, Washington 99354, USA.
^¶Contact author: editorial-board@legend-exp.org; https://legend-exp.org.
^**Institutional Board membership suspended since April 26, 2022.
^††Deceased.

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Phys. Rev. Lett. 136, 022701 – Published 16 January, 2026

DOI: https://doi.org/10.1103/25tk-nctn

Abstract

The LEGEND Collaboration is searching for neutrinoless double-beta ( $0 ν β β$ ) 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 $0 ν β β$ 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 ${0.5}_{- 0.2}^{+ 0.3} cts / (keV ton yr)$ in the $0 ν β β$ 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 $2.8 \times 10^{26} yr$ on the half-life of $0 ν β β$ decay, reveals no evidence for a signal and sets a new observed lower limit at $T_{1 / 2}^{0 ν} > 1.9 \times 10^{26} yr$ (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 $m_{β β} < 75 - 200 meV$ , depending on the adopted nuclear matrix element.

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Article Text

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Phys. Rev. Lett. 136, 022701– Published 16 January, 2026

Vol. 136, Iss. 2 — 16 January 2026

Received 21 May 2025
Revised 3 September 2025
Accepted 29 September 2025

DOI: https://doi.org/10.1103/25tk-nctn

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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

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

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