Search for Majoron-emitting modes of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Xe</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>136</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math> double beta decay with the complete EXO-200 dataset
S. Al Kharusi, G. Anton, I. Badhrees, P. S. Barbeau, D. Beck, V. Belov, Trilochan Bhatta, M. Breidenbach, T. Brunner, G. F. Cao, W. R. Cen, C. Chambers, B. T. Cleveland, Minor J. Coon, A. Craycraft, T. Daniels, L. Darroch, S. J. Daugherty, J. Davis, S. Delaquis, A. Der Mesrobian-Kabakian, R. DeVoe, J. Dilling, A. Dolgolenko, M. J. Dolinski, J. Echevers, W. M. Fairbank, D. Fairbank, J. Farine, Soheyla Feyzbakhsh, P. Fierlinger, D. Fudenberg, P. Gautam, R. Gornea, G. Gratta, C. Hall, E. V. Hansen, J. Hoessl, P. Hufschmidt, M. Hughes, A. Iverson, A. Jamil, C. E. Jessiman, M. J. Jewell, A. Johnson, A. Karelin, L. J. Kaufman, T. Koffas, R. Krücken, A. Kuchenkov, K.S. Kumar, Y. Lan, A. C. Larson, B. G. Lenardo, D. S. Leonard, G. S. Li, S. Li, Z. Li, C. Licciardi, Y. H. Lin, R. MacLellan, Thomas McElroy, Thilo Michel, B. Mong, David C. Moore, K. Murray, O. Njoya, O. Nusair, A. Odian, I. Ostrovskiy, Andréa Perna, A. Piepke, A. Pocar, F. Retière, A. L. Robinson, P.C. Rowson, D. Ruddell, J. Runge, Susann Schmidt, D. Sinclair, K. Skarpaas, A. K. Soma, V. Stekhanov, M. Tarka, S. Thibado, J. Todd, T. Tolba, T.I. Totev, R. Tsang, B. Veenstra, V. Veeraraghavan, P. Vogel, J. L. Vuilleumier, M. Wagenpfeil, J. Watkins, M. Weber, Liangjian Wen, U. Wichoski, Gerrit Wrede, Sen Wu
Abstract
A search for Majoron-emitting modes of the neutrinoless double beta decay of $^{136}\mathrm{Xe}$ is performed with the full EXO-200 dataset. This dataset consists of a total $^{136}\mathrm{Xe}$ exposure of $234.1\text{ }\text{ }\mathrm{kg}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{yr}$, and includes data with detector upgrades that have improved the energy threshold relative to previous searches. A lower limit of ${\mathrm{T}}_{1/2}^{^{136}\mathrm{Xe}}>4.3\ifmmode\times\else\texttimes\fi{}{10}^{24}\text{ }\text{ }\mathrm{yr}$ 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 and a factor of 1.6 more stringent than the previous best limit from KamLAND-Zen. This limit corresponds to a constraint on the Majoron-neutrino coupling constant of $|⟨{g}_{ee}^{M}⟩|<(0.4--0.9)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$. 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-200 search. This search provides the most stringent limits to date on the Majoron-emitting decays of $^{136}\mathrm{Xe}$ with spectral indices $n=1$, 2, 3, and 7.