The measured half-life values for the transitions (Z,A)$~\rightarrow~$(Z+2,A) $+$ 2${{\mathit e}^{-}}$ $+$ 2${{\overline{\mathit \nu}}_{{{e}}}}$ to the 0${}^{+}$ ground state of the final nucleus are listed. We also list the transitions to an excited state of the final nucleus (0${}^{+}_{i}$, etc.). We report only the measuremetnts with the smallest (or comparable) uncertainty for each transition.

${\mathrm {\mathit t_{1/2}}}$ ($ 10^{20} $ yr) ISOTOPE TRANSITION METHOD DOCUMENT ID • • We do not use the following data for averages, fits, limits, etc. • • $ 20.22 \pm0.18 \pm0.38 $ ${}^{76}\mathrm {Ge}$ GERDA 1 AGOSTINI 2023 $ 1.11 {}^{+0.19}_{-0.14} {}^{+0.17}_{-0.15} $ ${}^{150}\mathrm {Nd}$ $0{}^{+} \rightarrow 0{}^{+}_{1}$ NEMO-3 2 AGUERRE 2023 $ 7.5 \pm0.8 {}^{+0.4}_{-0.3} $ ${}^{100}\mathrm {Mo}$ $0{}^{+} \rightarrow 0{}^{+}_{1}$ CUPID-Mo 3 AUGIER 2023 $ 0.0707 \pm0.0002 \pm0.0011 $ ${}^{100}\mathrm {Mo}$ CUPID-Mo 4 AUGIER 2023 A $ 0.869 \pm0.005 {}^{+0.009}_{-0.006} $ ${}^{82}\mathrm {Se}$ CUPID-0 5 AZZOLINI 2023 A $ 21.6 {}^{+6.2}_{-4.0} {}^{+4.0}_{-2.9} $ ${}^{136}\mathrm {Xe}$ NEXT 6 NOVELLA 2023 $ (219 \pm7) \times 10^{2} $ ${}^{128}\mathrm {Te}$ CUORE 7 ADAMS 2022 B $ 110 \pm20 \pm10 $ ${}^{124}\mathrm {Xe}$ XENON1T 8 APRILE 2022 A $ 118 \pm13 \pm14 $ ${}^{124}\mathrm {Xe}$ XENONnT 9 APRILE 2022 B $ 23.4 {}^{+0.8}_{-4.6} {}^{+3.0}_{-1.7} $ ${}^{136}\mathrm {Xe}$ NEXT 10 NOVELLA 2022 $ 8.76 {}^{+0.09}_{-0.07} {}^{+0.14}_{-0.17} $ ${}^{130}\mathrm {Te}$ CUORE 11 ADAMS 2021 $ 180 \pm50 \pm10 $ ${}^{124}\mathrm {Xe}$ 2${{\mathit \nu}}$DEC XENON1T 12 APRILE 2019 E $ 0.068 \pm0.0001 {}^{+0.0038}_{-0.0040} $ ${}^{100}\mathrm {Mo}$ NEMO-3 13 ARNOLD 2019 $ 0.939 \pm0.017 \pm0.058 $ ${}^{82}\mathrm {Se}$ NEMO-3 14 ARNOLD 2018 $ 0.263 {}^{+0.011}_{-0.012} $ ${}^{116}\mathrm {Cd}$ AURORA 15 BARABASH 2018 $ \text{> 0.87} $ ${}^{134}\mathrm {Xe}$ EXO-200 16 ALBERT 2017 C $ 8.2 \pm0.2 \pm0.6 $ ${}^{130}\mathrm {Te}$ CUORE-0 17 ALDUINO 2017 $ 0.274 \pm0.004 \pm0.018 $ ${}^{116}\mathrm {Cd}$ NEMO-3 18 ARNOLD 2017 $ 0.64 {}^{+0.07}_{-0.06} {}^{+0.12}_{-0.09} $ ${}^{48}\mathrm {Ca}$ NEMO-3 19 ARNOLD 2016 $ 0.0934 \pm0.0022 {}^{+0.0062}_{-0.0060} $ ${}^{150}\mathrm {Nd}$ NEMO-3 20 ARNOLD 2016 A $ 19.26 \pm0.94 $ ${}^{76}\mathrm {Ge}$ GERDA 21 AGOSTINI 2015 A $ 0.0693 \pm0.0004 $ ${}^{100}\mathrm {Mo}$ NEMO-3 22 ARNOLD 2015 $ 21.65 \pm0.16 \pm0.59 $ ${}^{136}\mathrm {Xe}$ EXO-200 23 ALBERT 2014 $ 92 {}^{+55}_{-26} \pm13 $ ${}^{78}\mathrm {Kr}$ BAKSAN 24 GAVRILYAK 2013 $ 23.8 \pm0.2 \pm1.4 $ ${}^{136}\mathrm {Xe}$ KamLAND-Z 25 GANDO 2012 A $ 7 \pm0.9 \pm1.1 $ ${}^{130}\mathrm {Te}$ NEMO-3 26 ARNOLD 2011 $ 0.235 \pm0.014 \pm0.016 $ ${}^{96}\mathrm {Zr}$ NEMO-3 27 ARGYRIADES 2010 $ 6.9 {}^{+1.0}_{-0.8} \pm0.7 $ ${}^{100}\mathrm {Mo}$ $0{}^{+} \rightarrow 0{}^{+}_{1}$ ${}^{}\mathrm {Ge}$ coinc. 28 BELLI 2010 $ 5.7 {}^{+1.3}_{-0.9} \pm0.8 $ ${}^{100}\mathrm {Mo}$ $0{}^{+} \rightarrow 0{}^{+}_{1}$ NEMO-3 29 ARNOLD 2007 $ 0.96 \pm0.03 \pm0.10 $ ${}^{82}\mathrm {Se}$ NEMO-3 30 ARNOLD 2005 A $ 0.29 {}^{+0.04}_{-0.03} $ ${}^{116}\mathrm {Cd}$ ${}^{}\mathrm {Cd}WO_{4}$ sc. 31 DANEVICH 2003 1  AGOSTINI 2023 report an updated value for the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ half-life of ${}^{76}\mathrm {Ge}$; the final result of the GERDA Phase II experiment. A subset of the data, corresponding to an exposure of exposure is 11.8 kg$\cdot{}$yr, is utilized. This is one of the most precise measurements of 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ decay reported in the literature. An effective nuclear matrix element of $0.101$ $\pm0.001$ is derived from this result. 2  AGUERRE 2023 report the results of a 5.25 yr search for the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ decay to the exited 0${}^{+}$ $\rightarrow$ 0${}^{+}_{1}$ state of the daughter nucleus, using the NEMO-3 tracking calorimeter. 36.6g of ${}^{150}\mathrm {Nd}$ isotope were available for the measurement of this decay rate. 3  AUGIER 2023 utilize the complete data, set collected by the CUPID-Mo bolometric calorimeter with particle ID and located at the LSM, to measure the ${}^{100}\mathrm {Mo}$ 2 ${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ half-life to excited 0${}^{+}_{1}$ state of the daughter nucleus. An exposure of 1.47 kg$\cdot{}$yr of ${}^{100}\mathrm {Mo}$ is available. 4  AUGIER 2023A use full data set collected by the CUPID-Mo experiment to derive an improved 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ g.s. to g.s. half-life of ${}^{100}\mathrm {Mo}$. An exposure of 1.48 kg$\cdot{}$yr of ${}^{100}\mathrm {Mo}$ is utilized. Supersedes ARMENGAUD 2020 . 5  AZZOLINI 2023A report an improved measurement of the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ decay with an exposure of 8.82 kg$\cdot{}$yr of ${}^{82}\mathrm {Se}$, collected with the CUPID-0 detector. Superseded AZZOLINI 2019B. 6  NOVELLA 2023 used the NEXT-White experiment, with a fiducial mass of 3.5 kg of enriched xenon, to measure the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ g.s. to g.s. half-life of ${}^{136}\mathrm {Xe}$. The experiment is based on a high-pressure gas TPC. Supersedes NOVELLA 2022. 7  ADAMS 2022B derive the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ half-life of ${}^{128}\mathrm {Te}$ from data of the CUORE bolometric calorimeter and the half-live ratio for ${}^{130}\mathrm {Te}$ $/$ ${}^{128}\mathrm {Te}$ reported in BERNATOWICZ 1992. 8  APRILE 2022A report an improved ${}^{124}\mathrm {Xe}$ 2${{\mathit \nu}}$DEC half-life measurement for ${}^{124}\mathrm {Xe}$, using data collected by the XENON1T detector with an isotopically not enriched Xe target. The analyzed ${}^{124}\mathrm {Xe}$ exposure is 0.87 kg$\cdot{}$yr. The statistical significance of the signal is 7.0 sigma. The stated half-life considers captures from the K shell up to the N5 shell.This result supersedes APRILE 2019E, which exclusively considered captures from the K shell. 9  APRILE 2022B use data collected by the XENONnT dark matter experiment to derive an improved ${}^{124}\mathrm {Xe}$ 2${{\mathit \nu}}$DEC half-life measurement for ${}^{124}\mathrm {Xe}$. This result supersedes APRILE 2022A. 10  NOVELLA 2022 report on a high-pressure gas TPC at Canfranc underground laboratory, filled with 3.5 kg (fiducial) xenon gas, used to measure the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ decay of ${}^{136}\mathrm {Xe}$. Topological track reconstruction is utilized in the data analysis. The measurement is based on comparing runs with isotopically enriched and depleted xenon. Other measurements with smaller error exist. 11  ADAMS 2021 use 102.7 kg yr of ${}^{130}\mathrm {Te}$ exposure, collected by the CUORE bolometric detector at LNGS, to perform a measurement of the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ decay of ${}^{130}\mathrm {Te}$. The dataset is more than 10-times that collected by the CUORE-0 experiment. The result has been revised in ADAMS 2023A. Supersedes ALDUINO 2017. 12  APRILE 2019E report first measurement of two-neutrino double electron capture in ${}^{124}\mathrm {Xe}$ using the XENON1T detector with a 0.73 t-yr exposure. An excess of $126$ $\pm29$ events is observed at $64.3$ $\pm0.6$ keV decay energy, corresponding to $\sqrt {\Delta {{\mathit \chi}^{2}} }$ = 4.4 with respect to the background-only hypothesis. 13  ARNOLD 2019 use the NEMO-3 tracking calorimeter with 34.3 kg y exposure to determine the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ half-life of ${}^{100}\mathrm {Mo}$. Supersedes ARNOLD 2015. 14  ARNOLD 2018 use the NEMO-3 tracking detector to determine the 2 ${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ half-life of ${}^{82}\mathrm {Se}$. 0.93 kg of ${}^{82}\mathrm {Se}$ was observed for 5.25 y. The half-life value was obtained based on the single-state-dominance (SSD) hypothesis, preferred in this case by about 2 $\sigma $. Supersedes ARNOLD 2005A. 15  BARABASH 2018 use 1.162 kg of ${}^{116}\mathrm {Cd}WO_{4}$ scintillating crystals to obtain this value. Supersedes DANEVICH 2003 with analogous source and agrees with ARNOLD 2017 with the NEMO-3 detector. 16  ALBERT 2017C uses the EXO-200 detector that contains $19.098$ $\pm0.014\%$ admixture of ${}^{134}\mathrm {Xe}$ to search for the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ decay mode. The exposure is 29.6 kg$\cdot{}$year. The median sensitivity is $1.2 \times 10^{21}$ years. 17  ALDUINO 2017 use the CUORE-0 detector containing 10.8 kg of ${}^{130}\mathrm {Te}$ in 52 crystals of TeO$_{2}$. The exposure was 9.3 kg yr of ${}^{130}\mathrm {Te}$. This is a more accurate rate determination than in ARNOLD 2011 and BARABASH 2011A. 18  ARNOLD 2017 use the NEMO-3 tracking calorimeter, containing 410 grams of enriched ${}^{116}\mathrm {Cd}$ exposed for 5.26 years, to determine the half-life value. 19  ARNOLD 2016 use the NEMO-3 detector and a source of 6.99 g of ${}^{48}\mathrm {Ca}$. The half-life is based on 36.7 g year exposure. It is consistent, although somewhat longer, than the previous determinations of the half-life. Supersedes BARABASH 2011A. 20  ARNOLD 2016A use the NEMO-3 tracking calorimeter, containing 36.6 g of ${}^{150}\mathrm {Nd}$ exposed for 1918.5 days, to determine the half-life. Supersedes ARGYRIADES 2009. 21  AGOSTINI 2015A use 17.9 kg yr exposure of the GERDA calorimeter to derive an improved measurement of the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ decay half life of ${}^{76}\mathrm {Ge}$. 22  ARNOLD 2015 use the NEMO-3 tracking calorimeter with 34.3 kg yr exposure to determine the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$-half life of ${}^{100}\mathrm {Mo}$. Supersedes ARNOLD 2005A and ARNOLD 2004. 23  ALBERT 2014 use the EXO-200 tracking detector for a re-measurement of the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$-half life of ${}^{136}\mathrm {Xe}$. A nuclear matrix element of $0.0218$ $\pm0.0003$ MeV${}^{-1}$ is derived from this data. Supersedes ACKERMAN 2011. 24  GAVRILYAK 2013 use a proportional counter filled with ${}^{}\mathrm {Kr}$ gas to search for the 2${{\mathit \nu}}$2K decay of ${}^{78}\mathrm {Kr}$. Data with the enriched and depleted ${}^{}\mathrm {Kr}$ were used to determine signal and background. A 2.5${{\mathit \sigma}}$ excess of events obtained with the enriched sample is interpreted as an indication for the presence of this decay. 25  GANDO 2012A use a modification of the existing KamLAND detector. The ${{\mathit \beta}}{{\mathit \beta}}$ decay source/detector is 13 tons of enriched ${}^{136}\mathrm {Xe}$-loaded scintillator contained in an inner balloon. The 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ decay rate is derived from the fit to the spectrum between 0.5 and 4.8 MeV. This result is in agreement with ACKERMAN 2011. 26  ARNOLD 2011 use enriched ${}^{130}\mathrm {Te}$ in the NEMO-3 detector to measure the 2 ${{\mathit \nu}}{{\mathit \beta}{\mathit \beta}}$ decay rate. This result is in agreement with, but more accurate than ARNABOLDI 2003. 27  ARGYRIADES 2010 use $9.4$ $\pm0.2$ g of ${}^{96}\mathrm {Zr}$ in NEMO-3 detector and identify its 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ decay. The result is in agreement and supersedes ARNOLD 1999. 28  BELLI 2010 use enriched ${}^{100}\mathrm {Mo}$ with 4 HP ${}^{}\mathrm {Ge}$ detectors to record the 590.8 and 539.5 keV ${{\mathit \gamma}}$ rays from the decay of the 0${}^{+}_{1}$ state in ${}^{100}\mathrm {Ru}$ both in singles and coincidences. This result confirms the measurement of KIDD 2009 and ARNOLD 2007 and supersedes them. 29  First exclusive measurement of 2${{\mathit \nu}}$-decay to the first excited 0${}^{+}_{1}$-state of daughter nucleus. ARNOLD 2007 use the NEMO-3 tracking calorimeter to detect all particles emitted in decay. Result agrees with the inclusive (0 ${{\mathit \nu}}{+}$ 2 ${{\mathit \nu}}$) measurement of DEBRAECKELEER 2001. 30  ARNOLD 2005A use the NEMO-3 tracking detector to determine the 2 ${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ half-life of ${}^{82}\mathrm {Se}$ with high statistics and low background (389 days of data taking). Supersedes ARNOLD 2004. 31  DANEVICH 2003 is calorimetric measurement of 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ ground state decay of ${}^{116}\mathrm {Cd}$ using enrichedCdWO$_{4}$ scintillators. Agrees with EJIRI 1995 and ARNOLD 1996. Supersedes DANEVICH 2000.

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