Double beta decay, Majorana neutrinos, and neutrino mass

TLDR

Neutrinoless double beta decay, whose observation would profoundly impact particle physics, nuclear physics, astrophysics, and cosmology, is currently under intense theoretical and experimental scrutiny, with increasing sensitivity and improved nuclear theory making the field increasingly promising. The review examines the status and discovery potential of proposed experiments, emphasizing panel‑favored proposals, and discusses the challenges of calculating nuclear matrix elements that govern the decay. Even a nonobservation of neutrinoless double beta decay will provide useful constraints, while observation would immediately reveal key properties of the neutrino.

Abstract

The theoretical and experimental issues relevant to neutrinoless double beta decay are reviewed. The impact that a direct observation of this exotic process would have on elementary particle physics, nuclear physics, astrophysics, and cosmology is profound. Now that neutrinos are known to have mass and experiments are becoming more sensitive, even the nonobservation of neutrinoless double beta decay will be useful. If the process is actually observed, we will immediately learn much about the neutrino. The status and discovery potential of proposed experiments are reviewed in this context, with significant emphasis on proposals favored by recent panel reviews. The importance of and challenges in the calculation of nuclear matrix elements that govern the decay are considered in detail. The increasing sensitivity of experiments and improvements in nuclear theory make the future exciting for this field at the interface of nuclear and particle physics.