Simultaneous Measurement of Half-Life and Spectral Shape of ^115In β-decay with an Indium Iodide Cryogenic Calorimeter

Current bounds on neutrino Majorana mass are affected by significant uncertainties in the nuclear calculations for neutrinoless double-beta decay. A key issue for a data-driven improvement of the nuclear theory is the actual value of the axial coupling constant g_A, which can be investigated through forbidden β-decays. We present the first measurement of 4^th-forbidden β-decay of ^115In with a cryogenic calorimeter based on Indium Iodide. Exploiting the enhanced spectral shape method for the first time to this isotope, our study accurately determines simultaneously spectral shape, g_A, and half-life. The Interacting Shell Model, which best fits our data, indicates a half-life for this decay at T_1/2=(5.26±0.06) × 10^14,yr.