Overview

Experimental groups worldwide are working to develop detectors that may allow the observation of neutrinoless double-beta decay. At least one ton-scale experiment will likely be funded in the U.S., and more may be funded elsewhere. Research is well underway for detectors based on ⁷⁶Ge, ¹³⁶Xe, ¹³⁰Te, and ⁸²Se.

A double-beta decay observation would demonstrate that neutrinos are Majorana particles, provide information about the neutrino-mass scale and hierarchy, and address physics beyond the Standard Model (BSM). The rate of the decay, however, depends on matrix elements that cannot be measured. The matrix elements clearly depend on complex nuclear structure, but may also reflect particle and hadronic physics since the decay can proceed either through the exchange of a light Majorana neutrino or through the exchange of an exotic still-undiscovered heavy particle, in which case both particle physics and hadronic physics will be required. Clearly, to use either a positive or null experimental result to probe the mechanism and parameters of lepton number violation from, one must compute the matrix elements with reasonable accuracy.

The program is intended to bring together experts in effective field theory, many-body theory, BSM physics, and experiment to address outstanding problems associated with the matrix elements that govern neutrinoless double-beta decay. We will emphasize specific topics each week and hold both an initial and a concluding workshop. We encourage participation by scientists who have not yet worked on double beta decay but who are interested and/or have worked on related topics.

Major goals of the program:

1. Identification of a viable path towards significantly reduced uncertainty in the matrix elements governing neutrinoless double beta decay.
2. Development of collaborations to carry us along this path.
3. Clarification of the new physics that can contribute to or be constrained by double beta decay, and identification of experiments and calculations that will help with make this task easier.

Week 1 (June 13-16): Opening workshop June 13 and 14 on significance of double-beta decay and the interplay of nuclear theory, particle theory, cosmology, and experiment in understanding its consequences. Rest of week focuses on these overarching issues. There will be a $15 registration fee to attend the opening workshop. The registration fee includes participation in the workshop, lectures, and coffee breaks.

Week 2 (June 19-23): Ab initio nuclear structure for double-beta decay, interplay with more phenomenological methods. What is needed for good computation of transitions?

Week 3 (June 26-20): Overlap of effective field theory (EFT) and nuclear structure. The g_A problem and weak currents.

Week 4 (July 3-7): Heavy particle exchange: interplay of EFT, lattice QCD, and nuclear structure. Workshop on Lattice QCD Input for Neutrinoless Double-Beta Decay July 6 and 7. If you are interested in attending the workshop as well, please apply on the workshop page directly. There will be a $15 registration fee to attend the Lattice QCD workshop. The registration fee includes participation in the workshop, lectures, and coffee breaks.

Week 5 (July 10-14): Matrix element synthesis, closing workshop on testing calculations and on path forward July 13 and 14.