The search for no neutrinos

Abstract

Scientists have seen no sign of an elusive nuclear decay that could help to explain why the Universe is dominated by matter, rather than antimatter. An upgraded experiment continues the search with unprecedented sensitivity. See Letter p.47 The nature of neutrinos is one of the most puzzling aspects of particle physics. Most extensions of the Standard Model assume neutrinos to be their own antiparticles, known as Majorana fermions, in which case a very rare, and as yet undetected, radioactive decay called neutrinoless double-β decay should exist. To find a rare decay or to put more stringent limits on its existence, it is crucial to suppress background events. Here, the GERDA Collaboration reports a search for neutrinoless double-β decay in 35.6 kilograms of germanium-76. Via a clever vetoing system, the team make their search essentially background-free—a long-awaited accomplishment in the field. They determine a lower limit on the half-life of this decay of 5.3 × 1025 years. Their background suppression techniques should enable a background-free search up to a half-life sensitivity of around 1027 years in the near future.