Probing the Mechanism of Neutrinoless Double-Beta Decay in Multiple Isotopes

TL;DR

This paper explores how measurements of neutrinoless double-beta decay across multiple isotopes can distinguish underlying decay mechanisms, emphasizing the importance of precise nuclear matrix elements and a multi-isotope experimental approach.

Contribution

It demonstrates how multi-isotope measurements can resolve degeneracies in decay mechanisms and assesses the impact of reduced uncertainties in nuclear matrix elements.

Findings

Two-isotope measurements can partially resolve decay mechanism degeneracies.

Adding a third isotope measurement can fully break degeneracies.

Reducing uncertainties in nuclear matrix elements enhances mechanism discrimination.

Abstract

A large experimental program is being mounted to search for neutrinoless double-beta decay over the next decade. Multiple experiments using different target isotopes are being prepared to explore the whole parameter space allowed for inverted-ordered light neutrinos, and have the potential to make discoveries in several other scenarios, including normal-ordered light neutrinos and other exotic mechanisms. We investigate to what extent long-range and exotic short-range contributions may be distinguished by combining measurements of the decay half-life across isotopes. We demonstrate how measurements in two isotopes may facilitate a joint measurement up to a two-fold degeneracy, and how a further measurement in a third isotope may remove this degeneracy. We also highlight the precision of the nuclear matrix elements needed to convert half-lives into information on the underlying decay mechanism. Considering their correlations and uncertainties in the framework of a global Bayesian analysis, we assess the consequences of a possible future 10-fold reduction in uncertainties. Our work motivates an experimental program measuring neutrinoless double-beta decay in more than one isotope, as this would break parameter degeneracies and advance our understanding of particle physics beyond the Standard Model.