Article | Published:

Background-free search for neutrinoless double-β decay of 76Ge with GERDA

Nature volume 544, pages 4752 (06 April 2017) | Download Citation

Abstract

Many extensions of the Standard Model of particle physics explain the dominance of matter over antimatter in our Universe by neutrinos being their own antiparticles. This would imply the existence of neutrinoless double-β decay, which is an extremely rare lepton-number-violating radioactive decay process whose detection requires the utmost background suppression. Among the programmes that aim to detect this decay, the GERDA Collaboration is searching for neutrinoless double-β decay of 76Ge by operating bare detectors, made of germanium with an enriched 76Ge fraction, in liquid argon. After having completed Phase I of data taking, we have recently launched Phase II. Here we report that in GERDA Phase II we have achieved a background level of approximately 10−3 counts keV−1 kg−1 yr−1. This implies that the experiment is background-free, even when increasing the exposure up to design level. This is achieved by use of an active veto system, superior germanium detector energy resolution and improved background recognition of our new detectors. No signal of neutrinoless double-β decay was found when Phase I and Phase II data were combined, and we deduce a lower-limit half-life of 5.3 × 1025 years at the 90 per cent confidence level. Our half-life sensitivity of 4.0 × 1025 years is competitive with the best experiments that use a substantially larger isotope mass. The potential of an essentially background-free search for neutrinoless double-β decay will facilitate a larger germanium experiment with sensitivity levels that will bring us closer to clarifying whether neutrinos are their own antiparticles.

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Acknowledgements

The GERDA experiment is supported by the German Federal Ministry for Education and Research (BMBF), the German Research Foundation (DFG) via the Excellence Cluster Universe, the Italian Istituto Nazionale di Fisica Nucleare (INFN), the Max Planck Society (MPG), the Polish National Science Centre (NCN), the Russian Foundation for Basic Research (RFBR) and the Swiss National Science Foundation (SNF). These research institutions acknowledge internal financial support. GERDA was constructed and commissioned by the authors of refs 13 and 19. The GERDA Collaboration (https://www.mpi-hd.mpg.de/gerda/) thanks the directors and the staff of the LNGS for their support of the GERDA experiment.

Author information

Author notes

    • S. T. Belyaev

    Deceased.

Affiliations

  1. INFN Laboratori Nazionali del Gran Sasso and Gran Sasso Science Institute, Assergi, Italy

    • M. Agostini
    • , M. Balata
    • , V. D’Andrea
    • , N. Di Marco
    • , A. di Vacri
    • , M. Junker
    • , M. Laubenstein
    •  & C. Macolino
  2. Institut für Kern- und Teilchenphysik, Technische Universität Dresden, Dresden, Germany

    • M. Allardt
    • , A. Domula
    • , B. Lehnert
    • , B. Schneider
    • , T. Wester
    •  & K. Zuber
  3. National Research Centre “Kurchatov Institute”, Moscow, Russia

    • A. M. Bakalyarov
    • , S. T. Belyaev
    • , K. Gusev
    • , V. I. Lebedev
    •  & S. V. Zhukov
  4. Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, Russia

    • I. Barabanov
    • , S. Belogurov
    • , L. Bezrukov
    • , E. Doroshkevich
    • , O. Fedorova
    • , A. Gangapshev
    • , V. Gurentsov
    • , L. V. Inzhechik
    • , V. Kazalov
    • , V. N. Kornoukhov
    • , V. V. Kuzminov
    • , B. Lubsandorzhiev
    • , P. Moseev
    • , O. Selivanenko
    • , A. Veresnikova
    •  & E. Yanovich
  5. Physik Institut der Universität Zürich, Zurich, Switzerland

    • L. Baudis
    • , G. Benato
    • , A. Kish
    • , M. Miloradovic
    • , R. Mingazheva
    •  & M. Walter
  6. Max-Planck-Institut für Kernphysik, Heidelberg, Germany

    • C. Bauer
    • , A. Gangapshev
    • , J. Hakenmüller
    • , M. Heisel
    • , W. Hofmann
    • , T. Kihm
    • , A. Kirsch
    • , A. Klimenko
    • , K. T. Knöpfle
    • , M. Lindner
    • , A. Lubashevskiy
    • , W. Maneschg
    • , M. Salathe
    • , J. Schreiner
    • , B. Schwingenheuer
    • , H. Simgen
    • , A. Smolnikov
    • , V. Wagner
    •  & A. Wegmann
  7. Dipartimento di Fisica, Università Milano Bicocca, Milan, Italy

    • E. Bellotti
  8. INFN Milano Bicocca, Milan, Italy

    • E. Bellotti
    • , C. Cattadori
    •  & F. Salamida
  9. Institute for Theoretical and Experimental Physics, Moscow, Russia

    • S. Belogurov
    • , A. Chernogorov
    • , E. V. Demidova
    • , I. V. Kirpichnikov
    • , V. N. Kornoukhov
    •  & A. A. Vasenko
  10. Dipartimento di Fisica e Astronomia dell ‘Università di Padova, Padua, Italy

    • A. Bettini
    • , R. Brugnera
    • , A. Garfagnini
    • , S. Hemmer
    • , E. Medinaceli
    • , C. Sada
    •  & K. von Sturm
  11. INFN Padova, Padua, Italy

    • A. Bettini
    • , R. Brugnera
    • , A. Garfagnini
    • , S. Hemmer
    • , I. Lippi
    • , E. Medinaceli
    • , C. Sada
    • , L. Stanco
    •  & K. von Sturm
  12. Physik Department and Excellence Cluster Universe, Technische Universität München, Germany

    • T. Bode
    • , K. Gusev
    • , J. Janicskó Csáthy
    • , A. Lazzaro
    • , S. Schönert
    •  & C. Wiesinger
  13. Institute of Physics, Jagiellonian University, Cracow, Poland

    • D. Borowicz
    • , N. Frodyma
    • , M. Misiaszek
    • , K. Panas
    • , K. Pelczar
    • , M. Wojcik
    •  & G. Zuzel
  14. Joint Institute for Nuclear Research, Dubna, Russia

    • D. Borowicz
    • , V. Brudanin
    • , V. Egorov
    • , K. Gusev
    • , A. Klimenko
    • , O. Kochetov
    • , A. Lubashevskiy
    • , I. Nemchenok
    • , N. Rumyantseva
    • , E. Shevchik
    • , M. Shirchenko
    • , A. Smolnikov
    • , I. Zhitnikov
    •  & D. Zinatulina
  15. Max-Planck-Institut für Physik, Munich, Germany

    • A. Caldwell
    • , C. Gooch
    • , R. Kneißl
    • , H. Y. Liao
    • , B. Majorovits
    • , D. Palioselitis
    • , O. Schulz
    •  & L. Vanhoefer
  16. Physikalisches Institut, Eberhard Karls Universität Tübingen, Tübingen, Germany

    • R. Falkenstein
    • , K. Freund
    • , P. Grabmayr
    • , A. Hegai
    • , J. Jochum
    • , C. Schmitt
    •  & A.-K. Schütz
  17. European Commission, JRC-Geel, Geel, Belgium

    • M. Hult
    •  & G. Lutter
  18. INFN Laboratori Nazionali del Sud, Catania, Italy

    • L. Pandola
  19. Dipartimento di Fisica, Università degli Studi di Milano e INFN Milano, Milan, Italy

    • A. Pullia
    •  & S. Riboldi

Consortia

  1. The GERDA Collaboration

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    All authors contributed to the publication, being differently involved in the design and construction of the detector system, in its operation, and in the acquisition and analysis of data. All authors approved the final version of the manuscript. In line with collaboration policy, the authors are listed here alphabetically.

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    The author declare no competing financial interests.

    Reviewer Information Nature thanks P. Barbeau, L. Canonica and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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    https://doi.org/10.1038/nature21717

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