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

摘要

The effects of the enhancement of the axial-charge matrix element gamma(5) 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 epsilon(MEC) of the axial-charge matrix element, as well as on the value of the axial-vector coupling constant g(A) was found in the spectral shapes of Y-93, Sr-95, and Y-97. The importance of the spectrum of Cs-138 in the determination of gA is discussed. Half-life analyses in the A approximate to 95 and A approximate to 135 regions were done, and consistent results g(A) approximate to 0.90, 0.75, and 0.65, corresponding to the three enhancement scenarios epsilon(MEC) = 1.4, 1.7, and 2.0, were obtained. Connection to the reactor-antineutrino anomaly is pointed out. (C) 2018 The Authors. Published by Elsevier B.V.