Neutrinoless double beta decay is a hypothetical nuclear transition whose observation would demonstrate that neutrinos are their own antiparticles and that lepton number is not conserved, with far-reaching implications for the origin of neutrino mass and the matter–antimatter imbalance in the Universe. This review examines the theoretical foundations of this process and surveys the principal experimental strategies developed to search for it, focusing on their operating concepts, strengths, and limitations. We summarize the current experimental landscape by presenting the most sensitive results achieved so far and by outlining the complementary approaches pursued by different detection techniques. Finally, we discuss the future direction of the field, emphasizing the technological advances needed to reach substantially better sensitivities and, ultimately, to detect this rare phenomenon.
Andrea Giuliani (Tue,) studied this question.