Article | Published:

Search for Majorana neutrinos with the first two years of EXO-200 data

Nature volume 510, pages 229234 (12 June 2014) | Download Citation

Abstract

Many extensions of the standard model of particle physics suggest that neutrinos should be Majorana-type fermions—that is, that neutrinos are their own anti-particles—but this assumption is difficult to confirm. Observation of neutrinoless double-β decay (0νββ), a spontaneous transition that may occur in several candidate nuclei, would verify the Majorana nature of the neutrino and constrain the absolute scale of the neutrino mass spectrum. Recent searches carried out with 76Ge (the GERDA experiment) and 136Xe (the KamLAND-Zen and EXO (Enriched Xenon Observatory)-200 experiments) have established the lifetime of this decay to be longer than 1025 years, corresponding to a limit on the neutrino mass of 0.2–0.4 electronvolts. Here we report new results from EXO-200 based on a large 136Xe exposure that represents an almost fourfold increase from our earlier published data sets. We have improved the detector resolution and revised the data analysis. The half-life sensitivity we obtain is 1.9 × 1025 years, an improvement by a factor of 2.7 on previous EXO-200 results. We find no statistically significant evidence for 0νββ decay and set a half-life limit of 1.1 × 1025 years at the 90 per cent confidence level. The high sensitivity holds promise for further running of the EXO-200 detector and future 0νββ decay searches with an improved Xe-based experiment, nEXO.

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Acknowledgements

EXO-200 is supported by the DOE and NSF in the United States, NSERC in Canada, SNF in Switzerland, NRF in Korea, RFBR (12-02-12145) in Russia and the DFG Cluster of Excellence ‘Universe’ in Germany. EXO-200 data analysis and simulation used resources of the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office of Science of the US DOE under contract no. DE-AC02-05CH11231. The EXO-200 collaboration acknowledges the WIPP for their hospitality.

Author information

Affiliations

  1. Physics Department and CEEM, Indiana University, Bloomington, Indiana 47405, USA.

    • J. B. Albert
    • , S. J. Daugherty
    • , T. N. Johnson
    •  & L. J. Kaufman
  2. Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA.

    • D. J. Auty
    • , M. Hughes
    •  & A. Piepke
  3. Department of Physics, Duke University, and Triangle Universities Nuclear Laboratory (TUNL), Durham, North Carolina 27708, USA.

    • P. S. Barbeau
  4. Department of Physics, Laurentian University, Sudbury, Ontario P3E 2C6, Canada.

    • E. Beauchamp
    • , B. Cleveland
    • , J. Farine
    • , B. Mong
    •  & U. Wichoski
  5. Physics Department, University of Illinois, Urbana-Champaign, Illinois 61801, USA.

    • D. Beck
    • , M. Coon
    • , M. Tarka
    • , J. Walton
    •  & L. Yang
  6. Institute for Theoretical and Experimental Physics, Moscow 117218, Russia.

    • V. Belov
    • , A. Burenkov
    • , M. Danilov
    • , A. Dolgolenko
    • , A. Karelin
    • , A. Kuchenkov
    • , V. Stekhanov
    •  & O. Ya. Zeldovich
  7. Physics Department, Colorado State University, Fort Collins, Colorado 80523, USA.

    • C. Benitez-Medina
    • , C. Chambers
    • , A. Craycraft
    • , W. Fairbank Jr
    •  & T. Walton
  8. Physics Department, University of Massachusetts, Amherst, Massachusetts 01003, USA.

    • J. Bonatt
    • , T. Daniels
    • , S. Johnston
    • , K. S. Kumar
    • , A. Pocar
    •  & J. D. Wright
  9. Physics Department, Stanford University, Stanford, California 94305, USA.

    • J. Bonatt
    • , T. Brunner
    • , J. Chaves
    • , J. Davis
    • , R. DeVoe
    • , D. Fudenberg
    • , G. Gratta
    • , S. Kravitz
    • , D. Moore
    • , I. Ostrovskiy
    • , A. Rivas
    • , A. Schubert
    • , D. Tosi
    • , K. Twelker
    •  & M. Weber
  10. SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.

    • M. Breidenbach
    • , S. Herrin
    • , A. Johnson
    • , R. MacLellan
    • , A. Odian
    • , C. Y. Prescott
    • , P. C. Rowson
    • , J. J. Russell
    •  & A. Waite
  11. Institute of High Energy Physics, Beijing 100049, China.

    • G. F. Cao
    • , X. S. Jiang
    • , L. J. Wen
    •  & Y. B. Zhao
  12. SNOLAB, Sudbury, Ontario P3Y 1N2, Canada.

    • B. Cleveland
  13. Physics Department, University of Maryland, College Park, Maryland 20742, USA.

    • C. G. Davis
    • , C. Hall
    • , S. Slutsky
    •  & Y.-R. Yen
  14. LHEP, Albert Einstein Center, University of Bern, 3012 Bern, Switzerland.

    • S. Delaquis
    • , G. Giroux†
    • , R. Gornea
    • , T. Tolba
    •  & J.-L. Vuilleumier
  15. Department of Physics, Drexel University, Philadelphia, Pennsylvania 19104, USA.

    • M. J. Dolinski
    • , M. J. Jewell
    • , Y. H. Lin
    • , E. Smith
    •  & Y.-R. Yen
  16. Physics Department, Carleton University, Ottawa, Ontario K1S 5B6, Canada.

    • M. Dunford
    • , K. Graham
    • , R. Killick
    • , T. Koffas
    • , F. Leonard
    • , C. Licciardi
    • , C. Ouellet
    • , M. P. Rozo
    •  & D. Sinclair
  17. Technische Universität München, Physikdepartment, and Excellence Cluster Universe, 85748 Garching, Germany.

    • W. Feldmeier
    • , P. Fierlinger
    •  & M. G. Marino
  18. Department of Physics, University of Seoul, Seoul 130-743, South Korea.

    • D. S. Leonard
  19. Waste Isolation Pilot Plant, Carlsbad, New Mexico 88220, USA.

    • R. Nelson
  20. TRIUMF, Vancouver, British Columbia V6T 2A3, Canada.

    • D. Sinclair
  21. Kellogg Laboratory, Caltech, Pasadena, California 91125, USA

    • P. Vogel
  22. †Queen’s University, Kingston, Ontario K7L 3N6, Canada (G. Giroux); California Institute of Technology, Pasadena, California 91125, USA (S.S.); University of Wisconsin, Madison, Wisconsin 53706, USA (D.T.).

    • S. Slutsky
    •  & D. Tosi

Consortia

  1. The EXO-200 Collaboration

Authors

    Contributions

    Each of the authors participated in the collection and analysis of the data reported here, with the following exceptions: D.B. contributed to the slow controls system; G.F.C. performed energy resolution simulations; X.S.J. and Y.B.Z. provided electronics expertise; M. Danilov, A.D., T.K. and P.V. contributed to the initial conception and design of the experiment; M. Danilov and A.D. also contributed to the acquisition of the xenon, while P.V. also advised on nuclear and particle theory; J.D., R.N. and A.R. provided engineering, operations and technical support at the WIPP facility; A.J., J.J.R. and A.W. supported data acquisition, data processing and software. In line with collaboration policy, the authors are listed here alphabetically. EXO-200 was constructed and commissioned by the authors of refs 15 and 31.

    Competing interests

    The author declare no competing financial interests.

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    DOI

    https://doi.org/10.1038/nature13432

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