Mesonic enhancement of the weak axial charge and its effect on the half-lives and spectral shapes of first-forbidden J+↔J− decays

Abstract

The effects of the enhancement of the axial-charge matrix element γ5 were studied in medium heavy and heavy nuclei for first-forbidden J+ ↔ J− decay transitions using the nuclear shell model. Noticeable dependence on the enhancement MEC of the axial-charge matrix element, as well as on the value of the axial-vector coupling constant gA was found in the spectral shapes of 93Y, 95Sr, and 97Y. The importance of the spectrum of 138Cs in the determination of gA is discussed. Half-life analyses in the A ≈ 95 and A ≈ 135 regions were done, and consistent results gA ≈ 0.90, 0.75, and 0.65, corresponding to the three enhancement scenarios MEC = 1.4, 1.7, and 2.0, were obtained. Connection to the reactor-antineutrino anomaly is pointed out.