Abstract
Quenching of the weak axial strength g_A is discussed and relations of this quenching to the nuclear matrix elements of double beta decays are highlighted. An analysis of Gamow-Teller transitions in the mass range A=62-142 is presented and its results are compared with those of many previous works. The enhancement of the axial charge is discussed for first-forbidden pseudoscalar beta transitions. Higher-forbidden beta transitions are introduced and their role in determining the effective value of g_A is examined, in particular from the point of view of rge beta-decay half-lives and the shapes of electron spectra of forbidden non-unique beta transitions.
Highlights
Double β decay has been under intensive discussion for the last decades from the point of view of both nuclear theory and ββ-decay experiments
The high stakes involved in the detection of 0νββ decay have made the associated theoretical and experimental aspects highly important, in particular the calculation of the involved nuclear matrix elements (NMEs)
It seems that the fit to the average value of the mean experimental β-decay NMEs brings the results of the proton-neutron version of the QRPA (pnQRPA) analysis closer to those of the ISM, in particular for the heavy end of the presently discussed nuclei
Summary
Double β decay (ββ decay) has been under intensive discussion for the last decades from the point of view of both nuclear theory and ββ-decay experiments. The NMEs of 0νββ decays have been computed for decades using a number of different nuclear-structure approaches (for older calculations see the review [1] and for the more recent ones see [2, 3]). Besides the problems with the calculations of the NMEs of 0νββ decay there is an other severe problem, namely the one related to the value of the weak axial coupling gA. For the 0νββ decay the values of these weak couplings are altered by the high energy scale (q ∼ 100 MeV) of the exchanged momentum q between the decaying nucleons and the Majorana neutrino. The gA for higher multipoles can be studied through half-lives and electron spectral shapes of forbidden β decays, as discussed in section 4 of this article
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