New determination of double-beta-decay properties in 48Ca: high-precision Q-value measurement and improved nuclear matrix element calculations

TL;DR

This paper presents a precise measurement of the Q-value for 48Ca double-beta decay and introduces an improved nuclear matrix element calculation, enhancing the understanding of this decay process.

Contribution

The study provides the first high-precision Q-value measurement for 48Ca and develops an advanced shell-model calculation for the nuclear matrix element, incorporating second-order many-body perturbation theory.

Findings

Q-value measured as 4267.98(32) keV

Nuclear matrix element increased by about 75% with the new calculation

Results support the feasibility of 48Ca double-beta-decay experiments

Abstract

We report a direct measurement of the Q-value of the neutrinoless double-beta-decay candidate 48Ca at the TITAN Penning-trap mass spectrometer, with the result that Q = 4267.98(32) keV. We measured the masses of both the mother and daughter nuclides, and in the latter case found a 1 keV deviation from the literature value. In addition to the Q-value, we also present results of a new calculation of the neutrinoless double-beta-decay nuclear matrix element of 48Ca. Using diagrammatic many-body perturbation theory to second order to account for physics outside the valence space, we constructed an effective shell-model double-beta-decay operator, which increased the nuclear matrix element by about 75% compared with that produced by the bare operator. The new Q-value and matrix element strengthen the case for a 48Ca double-beta-decay experiment.