Final Results of GERDA on the Search for Neutrinoless Double-$\beta$ Decay

TL;DR

The GERDA experiment searched for neutrinoless double-beta decay in germanium-76, achieving extremely low background levels and setting a new lower limit on the decay half-life, with no signal observed.

Contribution

GERDA demonstrated unprecedented background suppression and collected a large exposure, providing the most stringent limit to date on neutrinoless double-beta decay in $^{76}$Ge.

Findings

No evidence of neutrinoless double-beta decay was observed.

Set a lower limit on the half-life at 1.8×10^{26} years.

Achieved a background index of 5.2×10^{-4} counts/(keV·kg·yr).

Abstract

The GERmanium Detector Array (GERDA) experiment searched for the lepton-number-violating neutrinoless double-$\beta$ ($0\nu\beta\beta$) decay of $^{76}$Ge, whose discovery would have far-reaching implications in cosmology and particle physics. By operating bare germanium diodes, enriched in $^{76}$Ge, in an active liquid argon shield, GERDA achieved an unprecedently low background index of $5.2\times10^{-4}$ counts/(keV$\cdot$kg$\cdot$yr) in the signal region and met the design goal to collect an exposure of 100 kg$\cdot$yr in a background-free regime. When combined with the result of Phase I, no signal is observed after 127.2 kg$\cdot$yr of total exposure. A limit on the half-life of $0\nu\beta\beta$ decay in $^{76}$Ge is set at $T_{1/2}>1.8\times10^{26}$ yr at 90% C.L., which coincides with the sensitivity assuming no signal.