Abstract:
We report the observation of two-neutrino double-beta decay in ¹³⁶Xe with T₁/₂ = 2.11 ± 0.04(stat) ± 0.21(syst) × 10²¹ yr. This second-order process, predicted by the standard model, has been observed for several nuclei but not for ¹³⁶Xe. The observed decay rate provides new input to matrix element calculations and to the search for the more interesting neutrinoless double-beta decay, the most sensitive probe for the existence of Majorana particles and the measurement of the neutrino mass scale.
