The GERDA Experiment in the Search for Neutrinoless Double-Beta Decay

An open question still involves the nature of neutrinos: are they equal to their anti-matter counterpart? The most promising way to test this Majorana nature of neutrinos is searching for the neutrinoless double beta decay (0 nu beta beta), a hypothetical lepton number violating nuclear process. Furthermore, its observation would give an extraordinary insight into why our universe is predominantly composed of matter, which is another unsolved puzzle of cosmology and particle physics. Since 2011, the Gerda collaboration has searched for 0 nu beta beta of Ge-76 by operating bare germanium detectors, enriched in the double-beta decaying isotope Ge-76, in liquid argon. Exploiting the combination of excellent energy resolution of germanium detectors and scintillating properties of argon, the Gerda experiment succeeded to achieve an unprecedented background-free regime. In December 2019, after fulfilling and exceeding the design goals of the experiment, data taking was stopped. No signal has been observed, hence a lower limit on the half-life of 0 nu beta beta in Ge-76 has been set at T-1/2(0 nu) > 1.8 x 10(26) years at 90% C.L. The final results of the 12 Gerda experiment are discussed.