Double beta decay of128Te and130Te: Improved limit on the neutrino restmass

Abstract

Based on mass spectrometric determinations of128Xe and130Xe accumulated in a (1.31±0.14)×109 yrs old tellurium ore as a result of Double Beta Decay of128Te and130Te respectively, the Double Beta Decay rate ratio128λββ/130λββ is found to be $$\left( {1.03\begin{array}{*{20}c} { + 1.13} \\ { - 1.03} \\ \end{array} } \right) \times 10^{ - 4} $$ , where i λ= i λ0v + i λ2v is the sum of contributions from Majorana-and Dirac decay. In the frame of current Double Beta Decay theory, the result yields limits on the Majorana mass of the electron neutrino of $$\hat m_{v_e } \leqq 5.6$$ eV (95% confidence) and on the lepton non-conservation parameter η (right handed leptonic current admixture) of η≦2.4×10−5(2σ). Previously reported positive evidence for a neutrino restmass of ∼10 eV is contradicted by our results. Half lives areT 1/2(130Te)=(2.60±0.28)×1021 yrs andT 1/2(128Te) >8×1024yrs(2σ).