Measurement of the double-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="bold-italic">β</mml:mi></mml:mrow></mml:math>decay half-life of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mrow/><mml:mn>136</mml:mn></mml:msup></mml:math>Xe with the KamLAND-Zen experiment

Abstract

We present results from the KamLAND-Zen double-beta decay experiment based on an exposure of 77.6 days with 129 kg of ${}^{136}$Xe. The measured two-neutrino double-beta decay half-life of ${}^{136}$Xe is ${T}_{1/2}^{2\ensuremath{\nu}}=2.38\ifmmode\pm\else\textpm\fi{}0.02(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.14(\mathrm{syst})\ifmmode\times\else\texttimes\fi{}{10}^{21}$ yr, consistent with a recent measurement by EXO-200. We also obtain a lower limit for the neutrinoless double-beta decay half-life, ${T}_{1/2}^{0\ensuremath{\nu}}&gt;5.7\ifmmode\times\else\texttimes\fi{}{10}^{24}$ yr at 90$%$ confidence level (C. L.), which corresponds to almost a fivefold improvement over previous limits.