The Hunt for No Neutrinos

T he search for physics beyond the standard model—our current best description of fundamental particles and the interactions between them—is a top priority at high-energy particle accelerators. But researchers are also searching for new physics in the “low-energy” environment of the nucleus through a process known as neutrinoless double-beta (0νββ) decay. This hypothetical decay would show that neutrinos are their own antiparticles and that a fundamental law—the conservation of lepton number—is violated in nature. It would also explain why neutrinos are so light. Four experimental collaborations [1–4] are reporting new lower limits on the decay’s half-life, all of which exceed 1025 years. Several of these experiments should reach the 1026 level soon, thus catching up with a fifth experiment [5]. These new results invite a discussion of why detecting 0νββ decay is of interest and what physicists might learn as the experiments become more sensitive.