Analysis of ^115in Β Decay Through the Spectral Moment Method

We analyze the ^115In β-decay energy spectrum through the spectralmoment method (SMM), previously introduced in the context of ^113Cd βdecay. The spectral moments μ_n are defined as averaged n^ th powersof the β particle energy, characterizing the spectrum normalization(n=0) and shape (n≥ 1) above a given threshold. For ^115In, weconsider three independent datasets characterized by different thresholds. Wealso consider three nuclear model calculations with two free parameters: theratio of axial-vector to vector couplings, r=g_ A/g_ V, and thesmall vector-like relativistic nuclear matrix element (NME), s=s-NME. Byusing the most recent of the three datasets, we show that the first fewspectral moments can determine (r, s) values in good agreement with thoseobtained by full-fledged experimental fits. We then work out the SMM resultsfor the other datasets. We find that, although g_ A quenching isgenerally favored, the preferred quenching factors may differ considerablydepending on the chosen experimental data and nuclear models. We discussvarious issues affecting both the overall normalization and the low-energybehaviour of the measured and computed spectra, and their joint effects on theexperimentally quoted half-life values. Further ^115In β-decay dataat the lowest possible energy threshold appear to be crucial to clarify theseissues.