Discovering the Nature of Neutrinos: How Nuclear Theory Will Advance this Grand Endeavor

Kyle Wendt | 19-LW-039

Project Overview

Why is there more matter than antimatter in the visible universe? Are neutrinos their own antiparticles? These are some of the most profound questions in science. The detection of a neutrinoless double-beta decay and the measurement of its half-life is one of the most important experimental endeavors in science because it will answer these questions. Paramount to these measurements are accurate predictions with quantified uncertainties of neutrinoless-double-beta-decay nuclear transitions, especially for the germanium-76 and xeon-136 nuclei, two candidate materials for building the next generation of neutrinoless-double-beta-decay experiments.

In this project, we studied a specific, difficult-to-assess source of uncertainty that will affect upcoming microscopic predictions. This uncertainty arises from an incomplete yet systematically improvable model of interactions between nucleons, as well as interactions between nucleons and other particles involved in the decay process. We employed a surrogate model of the germanium-76 nucleus and its decay products, which was just detailed enough to adequately mimic the decaying nucleons and provide a reasonable measure of this uncertainty, avoiding the immense computational expense required in quantifying uncertainties of the full calculation. We found that microscopic calculations of this process can be expected to achieve relative theory uncertainties around 30 percent, including an unconstrained contribution that had the potential to spoil microscopic calculations. This results in a nearly order-of-magnitude improvement over previously estimated uncertainties for this rare decay process.

Mission Impact

Our surrogate model is being incorporated into the uncertainty analysis of the DOE topical collaboration on nuclear theory for double beta decay and fundamental symmetries, a multi-institutional uncertainty quantification effort. In addition, our project supports the neutrinoless Enriched Xenon Observatory (nEXO) experiment, a next-generation double-beta-decay experiment led by Lawrence Livermore National Laboratory. Insight gained through this project resulted in programmatic applications to augment nuclear data libraries used by applications, and to identify faulty nuclear data evaluations within a library. Our research also supports the Laboratory's core competency in nuclear, chemical, and isotopic science and technology.

Publications, Presentations, and Patents

Coello Pérez, E. A. 2019. "Toy model for germanium 76 neutrinoless double-beta decay." Bayesian Inference in Subatomic Physics - A Wallenberg Symposium, Gothenburg, Sweden, September 2019. LLNL-PRES-790618

——— 2019b. "Toy model for germanium 76 neutrinoless double-beta decay." Berkeley, CA, December 2019. LLNL-PRES-799238

——— 2020a."Neutrinoless double-beta decay of 76Ge with uncertainties from chiral EFT." Los Alamos National Laboratory, NM, February 2020. LLNL-PRES-804106

——— 2020b. "Theoretical uncertainty for neutrinoless double-beta decay from chiral EFT." American Physical Society 2020 meeting (online), April 2020. LLNL-PRES-808782

——— 2020c. "Theoretical uncertainty for neutrinoless double-beta decay from chiral EFT." DBD meeting, Lawrence Berkeley National Laboratory, Berkeley, CA, May 2020. LLNL-PRES-810767