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arXiv · 2511.13990

Search for Double Beta Decays of $^{134}$Xe with EXO-200 Phase II

S. Al Kharusi·G. Anton·I. Badhrees·P. S. Barbeau·V. Belov·T. Bhatta·M. Breidenbach·T. Brunner·G. F. Cao·W. R. Cen·C. Chambers·B. Cleveland·M. Coon·A. Craycraft·T. Daniels·L. Darroch·S. J. Daugherty·J. Davis·S. Delaquis·A. Der Mesrobian-Kabakian·R. DeVoe·A. Dolgolenko·M. J. Dolinski·J. Echevers·B. Eckert·W. Fairbank Jr.·D. Fairbank·J. Farine·S. Feyzbakhsh·P. Fierlinger·Y. S. Fu·D. Fudenberg·P. Gautam·R. Gornea·G. Gratta·C. Hall·E. V. Hansen·J. Hoessl·P. Hufschmidt·M. Hughes·A. Iverson·A. Jamil·C. Jessiman·M. J. Jewell·A. Johnson·A. Karelin·L. J. Kaufman·T. Koffas·R. Krücken·A. Kuchenkov·K. S. Kumar·Y. Lan·A. Larson·B. G. Lenardo·D. S. Leonard·G. S. Li·S. Li·Z. Li·C. Licciardi·Y. H. Lin·R. MacLellan·T. McElroy·T. Michel·B. Mong·D. C. Moore·K. Murray·O. Njoya·O. Nusair·A. Odian·I. Ostrovskiy·H. Peltz Smalley·A. Perna·A. Piepke·A. Pocar·F. Retière·A. L. Robinson·P. C. Rowson·S. 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·L. J. Wen·U. Wichoski·G. Wrede·S. X. Wu·Q. Xia
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Abstract

EXO-200 was a leading double beta decay experiment consisting of a single-phase, enriched liquid xenon time projection chamber filled with an admixture of 80.672% $^{136}$Xe and 19.098% $^{134}$Xe. The detector operated at WIPP between 2010 and 2018 and was designed to search for double beta decay of $^{136}$Xe. Data was acquired in two phases separated by a period of detector upgrades. We report on the search for $0νββ$ and $2νββ$ decay of $^{134}$Xe with Phase II EXO-200 data, with median 90% C.L. exclusion sensitivity $T_{1/2}^{0ν} \geq 3.7\times 10^{23}$ yr and $T_{1/2}^{2ν} \geq 2.6 \times 10^{21}$ yr, respectively. No statistically significant signal is observed for either decay mode. We set a world-leading lower limit on the half-life of the neutrinoless decay mode of $^{134}$Xe of $T_{1/2}^{0ν} \geq 8.7\times10^{23}$ (90% C.L.) and the second strongest constraint on the two-neutrino decay of $T_{1/2}^{2ν} \geq 2.9\times10^{21}$ (90% C.L.), a 3-fold improvement over the EXO-200 Phase I measurement. New constraints are also set for the $2νββ$ and $0νββ$ decays of $^{134}$Xe to the lowest excited state of $^{134}$Ba.

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S. Al Kharusi, G. Anton, I. Badhrees, P. S. Barbeau, V. Belov, T. Bhatta, M. Breidenbach, T. Brunner, G. F. Cao, W. R. Cen, C. Chambers, B. Cleveland, M. Coon, A. Craycraft, T. Daniels, L. Darroch, S. J. Daugherty, J. Davis, S. Delaquis, A. Der Mesrobian-Kabakian, R. DeVoe, A. Dolgolenko, M. J. Dolinski, J. Echevers, B. Eckert, W. Fairbank Jr., D. Fairbank, J. Farine, S. Feyzbakhsh, P. Fierlinger, Y. S. Fu, D. Fudenberg, P. Gautam, R. Gornea, G. Gratta, C. Hall, E. V. Hansen, J. Hoessl, P. Hufschmidt, M. Hughes, A. Iverson, A. Jamil, C. Jessiman, M. J. Jewell, A. Johnson, A. Karelin, L. J. Kaufman, T. Koffas, R. Krücken, A. Kuchenkov, K. S. Kumar, Y. Lan, A. Larson, B. G. Lenardo, D. S. Leonard, G. S. Li, S. Li, Z. Li, C. Licciardi, Y. H. Lin, R. MacLellan, T. McElroy, T. Michel, B. Mong, D. C. Moore, K. Murray, O. Njoya, O. Nusair, A. Odian, I. Ostrovskiy, H. Peltz Smalley, A. Perna, A. Piepke, A. Pocar, F. Retière, A. L. Robinson, P. C. Rowson, S. 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, L. J. Wen, U. Wichoski, G. Wrede, S. X. Wu, Q. Xia. 2025-11-17. Search for Double Beta Decays of $^{134}$Xe with EXO-200 Phase II. https://doi.org/10.1103/vpny-23wq

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