Progress in the Study of Double Beta Decay

Abstract

This article reviews the history, theoretical framework, and experimental landscape of double beta decay, tracing how recent progress has driven a particular focus on the specific channel known as neutrino-less double beta decay (0νββ). Originally proposed by Wendell Furry in 1939 as a test of Ettore Majorana’s neutrino hypothesis, 0νββ has evolved from a “failed hypothesis” of the mid-20th century into the primary laboratory probe for physics beyond the Standard Model. The process—a hypothetical nuclear transition (A,Z)→(A,Z+2)+2e−—is the only known experimental avenue to confirm the Majorana nature of neutrinos and the non-conservation of total lepton number. The article explores the “chiral mask” that suppresses the decay rate, the connection between the half-life and the effective Majorana mass (mββ), and the critical role of nuclear matrix elements. Finally, it surveys the transition toward ton-scale detectors (e.g., LEGEND, nEXO, and CUPID) and argues for a conceptual shift in terminology: from the “privative” definition of “neutrinoless” to the affirmative observation of “matter creation” in the laboratory.