Determining <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>g</mml:mi></mml:mrow><mml:mrow><mml:mi>A</mml:mi></mml:mrow></mml:msub><mml:mo stretchy="false">/</mml:mo><mml:msub><mml:mrow><mml:mi>g</mml:mi></mml:mrow><mml:mrow><mml:mi>V</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math> with High-Resolution Spectral Measurements Using a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>LiInSe</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> Bolometer
A. Leder, D. Mayer, Jonathan Ouellet, F.A. Danevich, L. Dumoulin, A. Giuliani, Joel Kostensalo, J. Kotila, P. de Marcillac, C. Nones, V. Novati, E. Olivieri, D. V. Poda, J. Suhonen, V.I. Tretyak, L. A. Winslow, A. Zolotarova
Abstract
Neutrinoless double beta decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) 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 $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ experiments. In this Letter, we present measurements performed on a high-resolution ${\mathrm{LiInSe}}_{2}$ bolometer in a ``$\text{source}=\text{detector}$'' configuration to measure the spectral shape of the fourfold forbidden $\ensuremath{\beta}$ decay of $^{115}\mathrm{In}$. The value of ${g}_{A}/{g}_{V}$ is determined by comparing the spectral shape of theoretical predictions to the experimental $\ensuremath{\beta}$ 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 $>5\ensuremath{\sigma}$ with a model-dependent quenching factor of $0.655\ifmmode\pm\else\textpm\fi{}0.002$ as compared to the free-nucleon value for the interacting shell model. We also measured the $^{115}\mathrm{In}$ half-life to be $[5.18\ifmmode\pm\else\textpm\fi{}0.06(\mathrm{stat}{)}_{\ensuremath{-}0.015}^{+0.005}(\mathrm{sys})]\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{ }\mathrm{yr}$ within the interacting shell model framework. This Letter demonstrates the power of the bolometeric technique to perform precision nuclear physics single-$\ensuremath{\beta}$ decay measurements, which along with improved nuclear modeling can help reduce the uncertainties in the calculation of several decay nuclear matrix elements including those used in $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ sensitivity calculations.