A background-free search for neutrinoless double-β (0nββ) decay - a radioactive decay that, if found, would prove that neutrinos are their own antiparticles - is presented in this week’s Nature.

Certain extensions of the Standard Model of particle physics explain the dominance of matter over antimatter in the Universe by assuming that neutrinos are their own antiparticles. If this holds true, then a form of radioactive decay called 0nββ decay - in which an atomic nucleus decays and emits two electrons and no neutrinos - should exist. However, because the half-life for 0nββ decay is at least 15 orders of magnitude longer than the age of the Universe, its observation would require the suppression of all background signals that may interfere with its detection.

The GERDA (GERmanium Detector Array) Collaboration report the first data from Phase II of the GERDA experiment, in which they have searched for 0nββ decay in 35.6 kilograms of the isotope 76Ge. By using a system that vetoes background events, the authors report that they have achieved the first background-free experiment in the field. However, they have found no hint of 0nββ decay.

In an accompanying News & Views article, Phillip Barbeau notes that the background-free result is “a remarkable achievement for the field, suggesting that future searches will be highly sensitive to 0nββ decay.”