Simultaneous Measurement of Half-Life and Spectral Shape of $^{115}$In $\beta$-decay with an Indium Iodide Cryogenic Calorimeter

TL;DR

This study measures the half-life and spectral shape of $^{115}$In beta decay using a cryogenic calorimeter, providing insights into nuclear physics and neutrino properties.

Contribution

First simultaneous measurement of spectral shape, half-life, and axial coupling constant $g_A$ for $^{115}$In beta decay using a cryogenic Indium Iodide detector.

Findings

Half-life determined as (5.26 ± 0.06) × 10^{14} years.

Spectral shape and $g_A$ value obtained, aligning with the Interacting Shell Model.

Enhanced spectral shape method successfully applied to this isotope.

Abstract

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 $\beta$-decays. We present the first measurement of 4$^{th}$-forbidden $\beta$-decay of $^{115}$In 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 $T_{1/2}=(5.26\pm0.06) \times 10^{14}$,yr.