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Search for Double Beta Decays of¹³⁴ Xe with EXO-200 Phase II
Preprint

Search for Double Beta Decays of¹³⁴ 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, …
ArXiv.org
17 Nov 2025
DOI: https://doi.org/10.48550/arxiv.2511.13990
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https://arxiv.org/pdf/2511.13990View
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Abstract

Physics - Nuclear Experiment
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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