Lawrence Livermore National Laboratory



Kyle Wendt

Overview

Reliable model-independent predictions of nuclear processes such as beta-decay and neutrino-nucleus scattering are important for many fundamental science and mission-related investigations. For example, accurate descriptions of beta-decay are required for modeling the anti-neutrino spectrum of nuclear reactors, whether for detecting new physics such as sterile neutrinos, or remotely identifying the purpose of that reactor. For these activities, we need accurate calculations, as well as careful and thorough analyses of theoretical error and uncertainty in the underlying models and the many-body methods and codes used in solving that model. Unfortunately, modern theoretical calculations of these processes are inadequate for this task. At the heart of this inadequacy is the interaction between nucleons and other particles known as nuclear currents. Historically, descriptions of nuclear currents took into account only the simplest of particle interactions. Recently, the development of an effective field theory (EFT) known as chiral EFT has been used to derive large corrections to these particle interactions. However, the complex nature of these corrections inhibited their use in ab initio methods of predicting nuclear processes.

We developed a novel method to address these complexities and applied it in a series of benchmark and demonstrative calculations using state-of-the-art quantum few-nucleon solvers. Specifically, we studied the role of two-nucleon currents in electroweak processes using light nuclei, i.e., nuclei containing fewer than five nucleons, as a workbench to compute these processes and quantify their uncertainties using Bayesian extensions of the EFT.

Impact on Mission

The uncertainty quantification machinery built for this project is also being integrated into other nuclear ab initio frameworks at Lawrence Livermore National Laboratory, setting the stage for light-ion nuclear data evaluations that include a complete quantification of their theoretical uncertainties. This advances the Laboratory's core competencies in nuclear, chemical, and isotopic science and technology and supports Livermore's energy and counterterrorism mission areas.

Publications, Presentations, Etc.

Gysbers, P., et al. 2019. "Discrepancy Between Experimental and Theoretical Decay Rates Resolved from First Principles." Nature Physics 15: 428–431. doi:10.1038/s41567-019-0450-7. LLNL-JRNL-745901.

Hernandez, O., et al. 2017. "Recent Developments in Nuclear Structure Theory: An Outlook on the Muonic Atom Program." PoS Bormio 2017 041. LLNL-PROC-742212.

Wendt, K. A. 2018. "Novel Method for Computing the Tensor Multipole Expansion of Two Nucleon Currents in Momentum Space." 5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan. LLNL-PRES-760401.

——— . 2018. "A Novel Approach to Compute the Momentum Space Partial Wave Expansion of Two/Few-Body Currents." ECT Program on Electroweak Currents. LLNL-PRES-750865.

——— . 2018. "Towards a Quantitative Ab Initio Theory of Neutrinoless Double Beta Decay." INT Program on Neutrinoless Double-Beta Decay. LLNL-PRES-747866.