https://biblio.ugent.be/publication/685594/file/1130605.pdf

Review of Particle Physics

/pdf/review-of-particle-physics-1996-1997-jeg703df6k.pdf

Review of Particle Physics, 1996-1997

New results for the double beta decay of 76
Ge are presented. They are extracted from data obtained with the HEIDELBERG-MOSCOW experiment, which operates five enriched 76
Ge detectors in an extreme low-level environment in the Gran Sasso underground laboratory. The two-neutrino-accompanied double beta decay is evaluated for the first time for all five detectors with a statistical significance of 47.7 kg y resulting in a half-life of T
1/2
2ν = [1.55±0.01(stat)+0.19
-0.15(syst)]×1021 y. The lower limit on the half-life of the 0νββ decay obtained with pulse shape analysis is T
1/2
0ν > 1.9×1025(3.1×1025) y with 90% C.L. (68% C.L.) (with 35.5 kg y). This results in an upper limit of the effective Majorana-neutrino mass of 0.35 eV (0.27 eV) using the matrix elements of A. Staudt et al.'s work (Europhys. Lett. 13, 31 (1990)). This is the most stringent limit at present from double beta decay. No evidence for a majoron-emitting decay mode is observed.

Latest Results from the Heidelberg-Moscow Double Beta Decay Experiment

The data of the Heidelberg–Moscow double beta decay experiment for the measuring period August 1990–May 2000 (54.9813 kg y or 723.44 molyears), published recently, are analyzed using the potential of the Bayesian method for low counting rates. First evidence for neutrinoless double beta decay is observed giving first evidence for lepton number violation. The evidence for this decay mode is 97% (2.2σ) with the Bayesian method, and 99.8% c.l. (3.1σ) with the method recommended by the Particle Data Group. The half-life of the process is found with the Bayesian method to be $T_{1/2}^{0\nu} = (0.8\hbox{--}18.3)\times 10^{25}~{\rm y}$ (95% c.l.) with a best value of 1.5 × 1025y. The deduced value of the effective neutrino mass is, with the nuclear matrix elements from Ref. 1, = (0.11–0.56) eV (95% c.l.), with a best value of 0.39 eV. Uncertainties in the nuclear matrix elements may widen the range given for the effective neutrino mass by at most a factor 2. Our observation which at the same time means evide...

Evidence for neutrinoless double beta decay

Weak-interaction and nuclear-structure aspects of nuclear double beta decay

2ν and 0ν double-beta decay rates for all potential ββ emitters with A ≥ 70 are predicted. The nuclear transition matrix elements are calculated within the QRPA with a realistic effective nucleon-nucleon interaction. The results for neutrinoless decays are rather insensitive to details of the nuclear structure, except for the cases of 70Zn, 100Mo and 148Nd.

K. Muto

Papers

Calculation of 2ν and 0ν Double-Beta Decay Rates