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arXiv · 2303.01103

Search for Two-neutrino Double-Beta Decay of $^{136}\rm Xe$ to the $0^+_1$ excited state of $^{136}\rm Ba$ with the Complete EXO-200 Dataset

200 Collaboration·S. Al Kharusi·G. Anton·I. Badhrees·P. S. Barbeau·D. Beck·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·J. Dilling·A. Dolgolenko·M. J. Dolinski·J. Echevers·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·A. Perna·A. Piepke·A. Pocar·F. Retière·A. L. Robinson·P. C. Rowson·J. Runge·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
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Abstract

A new search for two-neutrino double-beta ($2\nu\beta\beta$) decay of $^{136}\rm Xe$ to the $0^+_1$ excited state of $^{136}\rm Ba$ is performed with the full EXO-200 dataset. A deep learning-based convolutional neural network is used to discriminate signal from background events. Signal detection efficiency is increased relative to previous searches by EXO-200 by more than a factor of two. With the addition of the Phase II dataset taken with an upgraded detector, the median 90$\%$ confidence level half-life sensitivity of $2\nu\beta\beta$ decay to the $0^+_1$ state of $^{136}\rm Ba$ is $2.9 \times 10^{24}~\rm yr$ using a total $^{136}\rm Xe$ exposure of $234.1~\rm kg~yr$. No statistically significant evidence for $2\nu\beta\beta$ decay to the $0^+_1$ state is observed, leading to a lower limit of $T^{2\nu}_{1/2}(0^+ \rightarrow 0^+_1) > 1.4\times10^{24}~\rm yr$ at 90$\%$ confidence level, improved by 70$\%$ relative to the current world's best constraint.

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200 Collaboration, S. Al Kharusi, G. Anton, I. Badhrees, P. S. Barbeau, D. Beck, 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, J. Dilling, A. Dolgolenko, M. J. Dolinski, J. Echevers, 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, A. Perna, A. Piepke, A. Pocar, F. Retière, A. L. Robinson, P. C. Rowson, J. Runge, 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. 2023-03-02. Search for Two-neutrino Double-Beta Decay of $^{136}\rm Xe$ to the $0^+_1$ excited state of $^{136}\rm Ba$ with the Complete EXO-200 Dataset. https://doi.org/10.1088/1674-1137/aceee3

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