Determining $g_A/g_V$ with High Resolution Spectral Measurements Using an LiInSe${}_2$ Bolometer

Abstract

Neutrinoless Double-Beta decay (0$\hat{I}½{\hat{I}}^2{\hat{I}}^2$) processes sample a wide range of intermediate forbidden nuclear transitions, which may be impacted by quenching of the axial vector coupling constant ($g_A/g_V$), the uncertainty of which plays a pivotal role in determining the sensitivity reach of 0$\hat{I}½{\hat{I}}^2{\hat{I}}^2$ experiments. In this Letter, we present measurements performed on a high-resolution LiInSe${}_2$~ bolometer in a ''source=detector'' configuration to measure the spectral shape of the 4-fold forbidden ${\hat{I}}^2$-decay of ${}^{115}$In. The value of $g_A/g_V$ is determined by comparing the spectral shape of theoretical predictions to the experimental ${\hat{I}}^2$ spectrum taking into account various simulated background components as well as a variety of detector effects. We find evidence of quenching of $g_A/g_V$ at $>5\ddot{I}ƒ$ with a model-dependent quenching factor of $0.655\pm 0.002$ as compared to the free-nucleon value for the Interacting Shell Model. We also measured the ${}^{115}$In half-life to be [$5.18\pm 0.06(\text{stat.}{)}_{-0.015}^{+0.005}(\text{sys.})]\times {10}^{14}$ yr within the Interacting Shell Model framework. This work demonstrates the power of the bolometeric technique to perform precision nuclear physics single-${\hat{I}}^2$ decay measurements, which can help reduce the uncertainties in the calculation of $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ nuclear matrix elements.

7 Pages, 4 Figures, 2 Tables, Submitted to PRL