A. Nicholson et al., Heavy Physics Contributions to Neutrinoless Double Beta Decay from QCD, Phys. Rev. Lett. 121 (2018) no.17, 172501

The observation of neutrinoless double beta decay would be a definitive sign of new physics and would illuminate a mechanism for generating the observed excess of matter over anti-matter in the universe. Searches for this very rare decay place some of the strongest constraints on the search for new physics, and are therefore some of the most fascinating (and highest priority) experiments. In order to improve these constraints, and interpret a potential signal, we must understand how this new physics manifests inside large nuclei. To do this we must be able to make predictions regarding the strength of the prospective interactions directly from the Standard Model of particle physics.

With a computing allocation at LLNL and another through the DOE INCITE Program at ORNL, we have performed the first calculation of the dominant contribution to neutrinoless double beta decay arising from prospective short distance contributions, improving our understanding of this mechanism. As the theories used to describe nuclei improve, our result can be used to compute the full nuclear decay rate with our calculation as an input.

The calculations performed here are the first in an increasingly complex series of calculations that will provide a complete understanding of how prospective sources of new physics that drive neutrinoless double beta decay will manifest in nuclei. The foundational level calculations, like the one summarized here, utilize lattice QCD to compute the processes directly in terms of the quarks and gluons which bind into nucleons. These lattice QCD calculations are sufficiently challenging that they may only be performed in systems of two or perhaps up to four nucleons. The results will be matched onto theoretical calculations performed with neutrons and protons that can then be coupled onto calculations of nuclei. In this way, we will build a quantitative understanding of prospective neutrinoless double beta decay mechanisms rooted in the Standard Model.