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Published December 1, 2021 | Published + Accepted Version
Journal Article Open

Search for Majoron-emitting modes of ¹³⁶Xe double beta decay with the complete EXO-200 dataset


A search for Majoron-emitting modes of the neutrinoless double-beta decay of ¹³⁶Xe is performed with the full EXO-200 dataset. This dataset consists of a total ¹³⁶Xe exposure of 234.1 kg⋅yr, and includes data with detector upgrades that have improved the energy threshold relative to previous searches. A lower limit of T^(¹³⁶Xe)_(1/2) > 4.3 x 10²⁴ yr at 90% C.L. on the half-life of the spectral index n = 1 Majoron decay was obtained, a factor of 3.6 more stringent than the previous limit from EXO-200, corresponding to a constraint on the Majoron-neutrino coupling constant of |⟨g^M_(ee)⟩|<(0.4-0.9) x 10⁻⁵. The lower threshold and the additional data taken resulted in a factor 8.4 improvement for the n = 7 mode compared to the previous EXO search. This search provides the most stringent limits to-date on the Majoron-emitting decays of 136Xe with spectral indices n = 1,2,3, and 7.

Additional Information

© 2021 The Author(s). 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. (Received 5 September 2021; accepted 17 November 2021; published 10 December 2021) EXO-200 is supported by the DOE and NSF in the USA, NSERC in Canada, SNF in Switzerland, IBS in Korea, RFBR in Russia, DFG in Germany, and CAS and ISTCP in China. The EXO-200 data analysis and simulation use resources of the National Energy Research Scientific Computing Center (NERSC). We gratefully acknowledge the KARMEN Collaboration for supplying the cosmic-ray veto detectors, as well as the WIPP for their hospitality. We would also like to thank Ricardo Cepedello for providing some of the energy spectra of two electrons for neutrinoless double beta decay of ¹³⁶Xe with nonstandard Majoron emission.

Attached Files

Accepted Version - 2109.01327.pdf

Published - PhysRevD.104.112002.pdf


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