Search for Majorana neutrinos with the first two years of EXO-200 data
200 Collaboration · Albert, J. B. · Auty, D. J. · Barbeau, P. S. · Beauchamp, E. · Beck, D. · Belov, V. · Benitez-Medina, C. · Bonatt, J. · Breidenbach, M. · Brunner, T. · Burenkov, A. · Cao, G. F. · Chambers, C. · Chaves, J. · Cleveland, B. · Coon, M. · Craycraft, A. · Daniels, T. · Danilov, M. · Daugherty, S. J. · Davis, C. G. · Davis, J. · DeVoe, R. · Delaquis, S. · Didberidze, T. · Dolgolenko, A. · Dolinski, M. J. · Dunford, M. · Fairbank Jr., W. · Farine, J. · Feldmeier, W. · Fierlinger, P. · Fudenberg, D. · Giroux, G. · Gornea, R. · Graham, K. · Gratta, G. · Hall, C. · Herrin, S. · Hughes, M. · Jewell, M. J. · Jiang, X. S. · Johnson, A. · Johnson, T. N. · Johnston, S. · Karelin, A. · Kaufman, L. J. · Killick, R. · Koffas, T. · Kravitz, S. · Kuchenkov, A. · Kumar, K. S. · Leonard, D. S. · Leonard, F. · Licciardi, C. · Lin, Y. H. · MacLellan, R. · Marino, M. G. · Mong, B. · Moore, D. · Nelson, R. · Odian, A. · Ostrovskiy, I. · Ouellet, C. · Piepke, A. · Pocar, A. · Prescott, C. Y. · Rivas, A. · Rowson, P. C. · Rozo, M. P. · Russell, J. J. · Schubert, A. · Sinclair, D. · Slutsky, S. · Smith, E. · Stekhanov, V. · Tarka, M. · Tolba, T. · Tosi, D. · Twelker, K. · Vogel, P. · Vuilleumier, J. -L. · Waite, A. · Walton, J. · Walton, T. · Weber, M. · Wen, L. J. · Wichoski, U. · Wright, J. D. · Yang, L. · Yen, Y. -R. · Zeldovich, O. Ya. · Zhao, Y. B.
Original · EN
Many extensions of the Standard Model of particle physics suggest that neutrinos should be Majorana-type fermions, but this assumption is difficult to confirm. Observation of neutrinoless double-beta 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 (GERDA experiment) and ¹³⁶Xe (KamLAND-Zen and EXO-200 experiments) have established the lifetime of this decay to be longer than 10²⁵ yr, corresponding to a limit on the neutrino mass of 0.2-0.4 eV. Here we report new results from EXO-200 based on 100 kg of ¹³⁶Xe exposure, representing an almost fourfold increase from our earlier published datasets. We have improved the detector resolution at the ¹³⁶Xe double-beta-decay Q-value to σ/E = 1.53% and revised the data analysis. The obtained half-life sensitivity is 1.9·10²⁵ yr, an improvement by a factor of 2.7 compared to previous EXO-200 results. We find no statistically significant evidence for 0νββ decay and set a half-life limit of 1.1·10²⁵ yr at 90% CL. The high sensitivity holds promise for further running of the EXO-200 detector and future 0νββ decay searches with nEXO.
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