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arXiv · 2008.06014

The Majorana Demonstrator's Search for Double-Beta Decay of $^{76}$Ge to Excited States of $^{76}$Se

I. J. Arnquist·F. T. Avignone III·A. S. Barabash·C. J. Barton·F. E. Bertrand·E. Blalock·B. Bos·M. Busch·M. Buuck·T. S. Caldwell·Y-D. Chan·C. D. Christofferson·P. -H. Chu·M. L. Clark·C. Cuesta·J. A. Detwiler·A. Drobizhev·T. R. Edwards·D. W. Edwins·Yu. Efremenko·H. Ejiri·S. R. Elliott·T. Gilliss·G. K. Giovanetti·M. P. Green·J. Gruszko·I. S. Guinn·V. E. Guiseppe·C. R. Haufe·R. Henning·D. Hervas Aguilar·E. W. Hoppe·A. Hostiuc·M. F. Kidd·I. Kim·R. T. Kouzes·A. M. Lopez·J. M. López-Castaño·E. L. Martin·R. D. Martin·R. Massarczyk·S. J. Meijer·S. Mertens·J. Myslik·T. K. Oli·G. Othman·L. S. Paudel·W. Pettus·A. W. P. Poon·D. C. Radford·A. L. Reine·K. Rielage·N. W. Ruof·B. Saykı·M. J. Stortini·D. Tedeschi·R. L. Varner·S. Vasilyev·J. F. Wilkerson·C. Wiseman·W. Xu·C. -H. Yu·B. X. Zhu
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Abstract

The Majorana Demonstrator is a neutrinoless double-beta decay search consisting of a low-background modular array of high-purity germanium detectors, $\sim2/3$ of which are enriched to 88\% in $^{76}$Ge. The experiment is also searching for double-beta decay of $^{76}$Ge to excited states (e.s.) in $^{76}$Se. $^{76}$Ge can decay into three daughter states of $^{76}$Se, with clear event signatures consisting of a $ββ$-decay followed by the prompt emission of one or two $γ$-rays. This results with high probability in multi-detector coincidences. The granularity of the Demonstrator detector array enables powerful discrimination of this event signature from backgrounds. Using 41.9~kg-y of isotopic exposure, the Demonstrator has set world leading limits for each e.s.\ decay of $^{76}$Ge, with 90\% CL lower half-life limits in the range of $(0.75-4.0)\times10^{24}$~y. In particular, for the $2ν$ transition to the first $0^+$ e.s.\ of $^{76}$Se, a lower half-life limit of $7.5\times10^{23}$~y at 90\% CL was achieved.

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I. J. Arnquist, F. T. Avignone III, A. S. Barabash, C. J. Barton, F. E. Bertrand, E. Blalock, B. Bos, M. Busch, M. Buuck, T. S. Caldwell, Y-D. Chan, C. D. Christofferson, P. -H. Chu, M. L. Clark, C. Cuesta, J. A. Detwiler, A. Drobizhev, T. R. Edwards, D. W. Edwins, Yu. Efremenko, H. Ejiri, S. R. Elliott, T. Gilliss, G. K. Giovanetti, M. P. Green, J. Gruszko, I. S. Guinn, V. E. Guiseppe, C. R. Haufe, R. Henning, D. Hervas Aguilar, E. W. Hoppe, A. Hostiuc, M. F. Kidd, I. Kim, R. T. Kouzes, A. M. Lopez, J. M. López-Castaño, E. L. Martin, R. D. Martin, R. Massarczyk, S. J. Meijer, S. Mertens, J. Myslik, T. K. Oli, G. Othman, L. S. Paudel, W. Pettus, A. W. P. Poon, D. C. Radford, A. L. Reine, K. Rielage, N. W. Ruof, B. Saykı, M. J. Stortini, D. Tedeschi, R. L. Varner, S. Vasilyev, J. F. Wilkerson, C. Wiseman, W. Xu, C. -H. Yu, B. X. Zhu. 2021-02-24. The Majorana Demonstrator's Search for Double-Beta Decay of $^{76}$Ge to Excited States of $^{76}$Se. https://doi.org/10.1103/physrevc.103.015501

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