Abstract
The theoretical and experimental study of the two-neutrino double-beta decay (2νββ-decay) is of crucial importance for reliable calculation of matrix elements governing the neutrinoless double-beta decay (0νββ-decay). That will allow to determine masses of neutrinos once the 0νββ-decay, which occurs if the neutrino is a massive Majorana particle and the total lepton number is not onserved, will be observed. Experiments studying the 2νββ-decay are currently approaching a qualitatively new level, where high-precision measurements are performed not only for half-lives but for all other observables of the process. In this context an improved formula for the 2νββ-decay is presented. Further, a novel approach for determining the effective axial-vector coupling constant is proposed.
Highlights
The observation of the neutrinoless double beta decay process (0νββ-decay) [1],(A, Z) → (A, Z + 2) + 2e−, (1)will demonstrate the Majorana nature of neutrinos but it will provide a measurement of the effective Majorana neutrino mass, mββ = Ue21m1 + Ue22m2 + Ue23m3. (2)Here, Uei and mi (i=1,2, and 3) are elements of the Pontecorvo-Maki-Nakagawa-Sakata neutrino mixing matrix and masses of neutrinos, respectively
Of the Gamow-Teller nuclear matrix elements, which depend on lepton energies
The standard treatment of the 2νββ-decay [1]: The calculation of the 2νββ-decay probability is usually simplified by neglecting the factors εK,L in energy denominators, what allows a separate calculation of the phase space factor and nuclear matrix element
Summary
Where M0ν, geAffand G0ν are the nuclear matrix element, effective axial-vector coupling constant, and phase-space factor, respectively. The 2νββ-decay has been a subject of experimental research for more than 60 years It has been detected for 12 different nuclei for transition to the ground state and in two cases to transition to 0+ excited state of the daughter nucleus [4]. This rare process is one of the major sources of background in running and planned experiments looking for a signal of the 0νββ-decay. A novel approach for determining the effective value of the axialvector coupling constant geAff is suggested
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