Towards precise and accurate calculations of neutrinoless double-beta decay

Abstract

We present the results of a National Science Foundation Project Scoping Workshop, the purpose of which was to assess the current status of calculations for the nuclear matrix elements governing neutrinoless double-beta decay and determine if more work on them is required. After reviewing important recent progress in the application of effective field theory, lattice quantum chromodynamics, and ab initio nuclear-structure theory to double-beta decay, we discuss the state of the art in nuclear-physics uncertainty quantification and then construct a roadmap for work in all these areas to fully complement the increasingly sensitive experiments in operation and under development. The roadmap includes specific projects in theoretical and computational physics as well as the use of Bayesian methods to quantify both intra- and inter-model uncertainties. The goal of this ambitious program is a set of accurate and precise matrix elements, in all nuclei of interest to experimentalists, delivered together with carefully assessed uncertainties. Such calculations will allow crisp conclusions from the observation or non-observation of neutrinoless double-beta decay, no matter what new physics is at play.

Theoretical Advances in Beta and Double-Beta Decay

“…Because of these uncertainties, there is a need for more fundamental approaches for the NME computation for DBD. In this regard, there is currently a coherent program for advancing such calculations [30], with the main idea being to obtain NME values with minimal dependence on the computational model and provide a quantified theoretical uncertainty. It is hoped that this will result in progress in developing methods based on particle and nuclear effective field theories (EFT) [31], lattice quantum chromodynamics (QCD) [32], and ab-initio nuclear-many-body techniques [33].…”

Theoretical Advances in Beta and Double-Beta Decay

“…Because of these uncertainties, there is a need for more fundamental approaches for the NME computation for DBD. In this regard, there is currently a coherent program for advancing such calculations [30], with the main idea being to obtain NME values with minimal dependence on the computational model and provide a quantified theoretical uncertainty. It is hoped that this will result in progress in developing methods based on particle and nuclear effective field theories (EFT) [31], lattice quantum chromodynamics (QCD) [32], and ab-initio nuclear-many-body techniques [33].…”

Improved Statistical Analysis for the Neutrinoless Double-Beta Decay Matrix Element of 136Xe

“…The normalized weights W k with k = svd, gcn, j5t can be obtained using the the Bayesian Model Averaging method [38,41] described in Section IV of Ref. [40].…”

“…Recently, there is a larger and consistent interest in the community to study these observables from a statistical point of view, thus considering fluctuation in the underlying nuclear dynamics and providing not only values for these observables, but also uncertainties [38]. In two recent papers [39,40] we applied this strategy to the 0νββ decay cases of 48 Ca and 136 Xe.…”

“…In particular, in Ref. [40] we analyzed the case M 0ν of 136 Xe using a a Bayesian Model Averaging approach [38,41]. The outcome was a range of values at 90% confidence level for the M 0ν NME, an expectation value and an uncertainty.…”