Validating Nuclear Physics Models with Precision Beta Decay Measurements

Forbidden non-unique beta decays are especially valuable to nuclear physics because their energy spectra are highly sensitive to nuclear structure details. Although theoretical models of these decays have improved significantly over the past several years, large uncertainties in their parameters remain a critical limitation. These uncertainties primarily stem from poorly constrained spectral shapes at low energies, where current measurements lack sufficient precision. Recent studies measuring energy spectra of beta decay electrons in long-lived isotopes, particularly Indium-115, have demonstrated a path toward reducing these theoretical uncertainties. While these studies have achieved unprecedented precision in half-life measurements, the persistent low-energy spectral constraints continue to limit the accuracy of theoretical models. We propose a new measurement of the beta decay spectrum of Indium-115 using transition edge sensors. These detectors will be faster than those used in previous measurements, providing better pile-up rejection and lower energy thresholds. In particular, better sensitivity to the beta decay spectrum at low energies will enable discrimination between nuclear models and tighter constraints on theoretical predictions. This talk will discuss the current state of precision spectral measurements and demonstrate how our improved experimental approach plans to address the remaining challenges in this field.