#### Half-life measurements of the two-neutrino double-$\beta$ decay

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.

${\mathrm {\mathit t_{1/2}}}$ ($10^{21}$ yr) ISOTOPE TRANSITION METHOD DOCUMENT ID
• • We do not use the following data for averages, fits, limits, etc. • •
$0.771 {}^{+0.008}_{-0.006} {}^{+0.012}_{-0.015}$ ${}^{130}\mathrm {Te}$ CUORE 1
 2021
$0.00712 {}^{+0.00018}_{-0.00014} \pm0.00010$ ${}^{100}\mathrm {Mo}$ CUPID-Mo 2
 2020
$18 \pm5 \pm1$ ${}^{124}\mathrm {Xe}$ 2${{\mathit \nu}}$ DEC XENON1T 3
 2019 E
$0.0068 \pm0.00001 {}^{+0.00038}_{-0.00040}$ ${}^{100}\mathrm {Mo}$ NEMO-3 4
 2019
$0.0860 \pm0.0003 {}^{+0.0019}_{-0.0013}$ ${}^{82}\mathrm {Se}$ CUPID-0 5
 2019 B
$0.0939 \pm0.0017 \pm0.0058$ ${}^{82}\mathrm {Se}$ NEMO-3 6
 2018
$0.0263 {}^{+0.0011}_{-0.0012}$ ${}^{116}\mathrm {Cd}$ AURORA 7
 2018
$\text{> 0.87}$ ${}^{134}\mathrm {Xe}$ EXO-200 8
 2017 C
$0.82 \pm0.02 \pm0.06$ ${}^{130}\mathrm {Te}$ CUORE-0 9
 2017
$0.00690 \pm0.00015 \pm0.00037$ ${}^{100}\mathrm {Mo}$ CUPID 10
 2017
$0.0274 \pm0.0004 \pm0.0018$ ${}^{116}\mathrm {Cd}$ NEMO-3 11
 2017
$0.064 {}^{+0.007}_{-0.006} {}^{+0.012}_{-0.009}$ ${}^{48}\mathrm {Ca}$ NEMO-3 12
 2016
$0.00934 \pm0.00022 {}^{+0.00062}_{-0.00060}$ ${}^{150}\mathrm {Nd}$ NEMO-3 13
 2016 A
$1.926 \pm0.094$ ${}^{76}\mathrm {Ge}$ GERDA 14
 2015 A
$0.00693 \pm0.00004$ ${}^{100}\mathrm {Mo}$ NEMO-3 15
 2015
$2.165 \pm0.016 \pm0.059$ ${}^{136}\mathrm {Xe}$ EXO-200 16
 2014
$9.2 {}^{+5.5}_{-2.6} \pm1.3$ ${}^{78}\mathrm {Kr}$ BAKSAN 17
 2013
$2.38 \pm0.02 \pm0.14$ ${}^{136}\mathrm {Xe}$ KamLAND-Zen 18
 2012 A
$0.7 \pm0.09 \pm0.11$ ${}^{130}\mathrm {Te}$ NEMO-3 19
 2011
$0.0235 \pm0.0014 \pm0.0016$ ${}^{96}\mathrm {Zr}$ NEMO-3 20
 2010
$0.69 {}^{+0.10}_{-0.08} \pm0.07$ ${}^{100}\mathrm {Mo}$ $0{}^{+} \rightarrow 0{}^{+}_{1}$ ${}^{}\mathrm {Ge}$ coinc. 21
 2010
$0.57 {}^{+0.13}_{-0.09} \pm0.08$ ${}^{100}\mathrm {Mo}$ $0{}^{+} \rightarrow 0{}^{+}_{1}$ NEMO-3 22
 2007
$0.096 \pm0.003 \pm0.010$ ${}^{82}\mathrm {Se}$ NEMO-3 23
 2005 A
$0.029 {}^{+0.004}_{-0.003}$ ${}^{116}\mathrm {Cd}$ ${}^{}\mathrm {Cd}WO_{4}$ scint. 24
 2003
 1 ADAMS 2021 use 102.7 kg yr of ${}^{130}\mathrm {Te}$ exposure, collected by the CUORE bolometric detector at LNGS, to perform the most precise measurement of 2${{\mathit \nu}}$ ${{\mathit \beta}}{{\mathit \beta}}$ decay of this nuclide to date. The dataset is more than 10-times that used by the CUORE-0 experiment. Supersedes ALDUINO 2017 .
 2 ARMENGAUD 2020 use the Li$_{2}{}^{100}\mathrm {Mo}O_{4}$ scintillating bolometers to determine the half-life of the 2${{\mathit \nu}}$ ${{\mathit \beta}}{{\mathit \beta}}$ decay of ${}^{100}\mathrm {Mo}$. The total exposure was 42.235 kg$\cdot{}$d. The single-state dominance for this decay is favored at $>$ 3 $\sigma$.
 3 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.
 4 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 .
 5 AZZOLINI 2019B use the CUPID-0 experiment, utilizing ZnSe bolometers and an exposure of 9.95 kg$\cdot{}$yr of ${}^{}\mathrm {Zn}{}^{82}\mathrm {Se}$, to determine the half-life of the 2${{\mathit \nu}}$ ${{\mathit \beta}}{{\mathit \beta}}$ decay of ${}^{82}\mathrm {Se}$. The analysis provides evidence for single state dominance showing that the higher state dominance is disfavored at the level of 5.5 ${{\mathit \sigma}}$ .
 6 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.
 7 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.
 8 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.
 9 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.
 10 ARMENGAUD 2017 use $185.9$ $\pm0.1$ g crystal of Li$_{2}{}^{100}\mathrm {Mo}{}^{}\mathrm {O}_{4}$ to determine the ${}^{100}\mathrm {Mo}$ 2${{\mathit \nu}}$ ${{\mathit \beta}}{{\mathit \beta}}$ half-life. The exposure was of $1303$ $\pm26$ hours only, using novel technique.
 11 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.
 12 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.
 13 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 .
 14 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 ${}^{76}\mathrm {Ge}$.
 15 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 .
 16 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 .
 17 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.
 18 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 .
 19 ARNOLD 2011 use enriched ${}^{130}\mathrm {Te}$ in the NEMO-3 detector to measure the 2 ${{\mathit \nu}}$ decay rate. This result is in agreement with, but more accurate than ARNABOLDI 2003 .
 20 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 .
 21 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.
 22 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 .
 23 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 .
 24 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 .
References:
PRL 126 171801 Measurement of the $2\nu\beta\beta$ Decay Half-Life of $^{130}\mathrm{Te}$ with CUORE
 ARMENGAUD 2020
EPJ C80 674 Precise measurement of $2\nu \beta \beta$ decay of $^{100}$Mo with the CUPID-Mo detection technology
 APRILE 2019E
NAT 568 532 Observation of two-neutrino double electron capture in $^{124}$Xe with XENON1T
 ARNOLD 2019
EPJ C79 440 Detailed studies of $^{100}$Mo two-neutrino double beta decay in NEMO-3
 AZZOLINI 2019B
PRL 123 262501
 ARNOLD 2018
EPJ C78 821 Final results on ${}^\mathbf 82 \hbox {Se}$ double beta decay to the ground state of ${}^\mathbf 82 \hbox {Kr}$ from the NEMO-3 experiment
 BARABASH 2018
PR D98 092007 Final results of the Aurora experiment to study $2\beta$ decay of $^{116}\mathrm{Cd}$ with enriched $^{116}\mathrm{Cd}{\mathrm{WO}}_{4}$ crystal scintillators
 ALBERT 2017C
PR D96 092001 Searches for Double Beta Decay of ${}^{134}\mathrm {Xe}$ with EXO-200
 ALDUINO 2017
EPJ C77 13 Measurement of the Two-Neutrino Double-Beta Decay Half-Life of ${}^{130}\mathrm {Te}$ with the CUORE-0 Experiment
 ARMENGAUD 2017
EPJ C77 785 Development of ${}^{100}\mathrm {Mo}$-containing Scintillating Bolometers for a High-sensitivity Neutrinoless Double-beta Decay Search
 ARNOLD 2017
PR D95 012007 Measurement of the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ Decay Half-Life and Search for the 0${{\mathit \nu}}$ $\beta \beta$ Decay of ${}^{116}\mathrm {Cd}$ with the NEMO-3 Detector
 ARNOLD 2016A
PR D94 072003 Measurement of the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ Decay Half-Life of ${}^{150}\mathrm {Nd}$ and a Search for 0${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ Decay Processes with the Full Exposure from the NEMO-3 Detector
 ARNOLD 2016
PR D93 112008 Measurement of the Double-Beta Decay Half-Life and Search for the Neutrinoless Double-Beta Decay of ${}^{48}\mathrm {Ca}$ with the NEMO-3 Detector
 AGOSTINI 2015A
EPJ C75 416 Results on ${{\mathit \beta}}{{\mathit \beta}}$ Decay with Emission of Two Neutrinos or Majorons in ${}^{76}\mathrm {Ge}$ from GERDA Phase I
 ARNOLD 2015
PR D92 072011 Results of the Search for Neutrinoless Double-${{\mathit \beta}}$ Decay in ${}^{100}\mathrm {Mo}$ with the NEMO-3 Experiment
 ALBERT 2014
PR C89 015502 An Improved Measurement of the 2${{\mathit \nu}}{{\mathit \beta}}{{\mathit \beta}}$ Half-life of ${}^{136}\mathrm {Xe}$ with EXO-200
 GAVRILYAK 2013
PR C87 035501 Indications of 2${{\mathit \nu}}$ 2${{\mathit K}}$ Capture in ${}^{78}\mathrm {Kr}$
 GANDO 2012A
PR C85 045504 Measurement of the Double-${{\mathit \beta}}$ Decay Half-Life of ${}^{136}\mathrm {Xe}$ with the KamLAND-Zen Experiment
 ARNOLD 2011
PRL 107 062504 Measurement of the ${{\mathit \beta}}{{\mathit \beta}}$ Decay Half-Life of ${}^{130}\mathrm {Te}$ with the NEMO-3 Detector
NP A847 168 Measurement of the Two Neutrino Double $\beta$ Decay Half-Life of ${}^{96}\mathrm {Zr}$ with the NEMO-3 Detector
NP A846 143 New Observation of 2${{\mathit \beta}}$ 2${{\mathit \nu}}$ Decay of ${}^{100}\mathrm {Mo}$ to the 0${}^{+}_{1}$ Level of ${}^{100}\mathrm {Ru}$ in the ARMONIA Experiment
NP A781 209 Measurement of Double beta Decay of ${}^{100}\mathrm {Mo}$ to Excited States in the NEMO-3 Experiment
PR C68 035501 Search for 2$\beta$ Decay of Cadmium and Tungsten Isotopes: Final Results of the Solotvina Experiment