Measurement of two-neutrino double electron capture half-life of 124^{124}Xe with PandaX-4T

Collaboration
Nov 21, 2024
18 pages
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Abstract: (arXiv)
Detailed studies of two-neutrino double electron capture (2ν\nuDEC) is a crucial step towards searching for the neutrino-less mode to explore the Majorana nature of neutrinos. We have measured precisely the half-life of the 2ν\nuDEC process in 124^{124}Xe, utilizing a total exposure of 1.73 tonne\cdotyear from the commissioning run and the first science run of the PandaX-4T experiment. A time-dependent background model in the O\mathcal{O}(10 keV) energy is constructed for the first time in PandaX-4T data. With an unbinned maximum likelihood fit, we determine the half-life of the 2ν\nuDEC process to be (1.03±0.15stat±0.06sys)×1022(1.03\pm0.15_{\rm stat}\pm0.06_{\rm sys})\times 10^{22}\,yr. Furthermore, we have evaluated the branching ratio for both electrons captured from the KK shell (KKKK) to be (65±5)%(65\pm5)\%, which aligns with the 124^{124}Xe nuclear model calculations within 1.5\,σ\sigma.
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  • 18 pages, 5 figures, 3 tables