Search for two-neutrino double-beta decay of 136Xe to the $$0$$$^{+}_{1}$$ excited state of 136Ba with the complete EXO-200 dataset
A new search for two-neutrino double-beta (2νββ) decay of 136Xe to the $$0_1^ + $$ excited state of 136Ba is performed with the full EXO-200 dataset. A deep learning-based convolutional neural network is used to discriminate signal from background events. Signal detection efficiency is increased relative to previous searches by EXO-200 by more than a factor of two. With the addition of the Phase II dataset taken with an upgraded detector, the median 90% confidence level half-life sensitivity of 2νββ decay to the $$0_1^ + $$ state of 136Ba is $$ 2.9 \times 10^{24} $$ yr using a total 136Xe exposure of 234.1 kg yr. Furthermore, no statistically significant evidence for 2νββ decay to the $$0_1^ + $$ state is observed, leading to a lower limit of $$ T^{2\nu}_{1/2}(0^+ \rightarrow 0^+_1) \gt 1.4\times10^{24} $$ yr at 90% confidence level, improved by 70% relative to the current world's best constraint.
- Research Organization:
- Univ. of Alabama, Tuscaloosa, AL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Nuclear Physics (NP)
- Contributing Organization:
- EXO-200 Collaboration
- Grant/Contract Number:
- FG02-01ER41166
- OSTI ID:
- 1999522
- Journal Information:
- Chinese Physics C, High Energy Physics and Nuclear Physics, Vol. 47, Issue 10; ISSN 1674-1137
- Publisher:
- IOP PublishingCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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