Speaker
Description
Observing the neutrino-less double-beta (0$\nu\beta\beta$) decay would imply that neutrinos have a Majorana mass component and provide evidence of lepton number violation. The Germanium Detector Array (GERDA) experiment searched for 0$\nu\beta\beta$ of $^{76}$Ge operating enriched high purity germanium detectors in an instrumented Liquid Argon volume at Laboratori Nazionali del Gran Sasso (LNGS) in Italy. At the end of Phase II, with a total exposure of 127.2 kg$\cdot$yr, no 0$\nu\beta\beta$ decay signal was found, and the most stringent lower limit on the $^{76}$Ge 0$\nu\beta\beta$ decay half-life was set at 1.8$\cdot$10$^{26}$ yr at 90% C.L., coinciding with the median sensitivity for the null hypothesis.
The ultra-low background and excellent understanding of the experiment’s response achieved in GERDA Phase II also allowed a measurement of the Standard Model 2$\nu\beta\beta$ decay half-life of $^{76}$Ge with unprecedented precision. It provides essential inputs for nuclear structure calculations that benefit the interpretation of 0$\nu\beta\beta$ decay results. Furthermore, the search for distortions of the 2$\nu\beta\beta$ decay spectrum allows exploring new physics, like 0$\nu\beta\beta$ decay with Majoron emission, Lorentz invariance, or search for sterile neutrinos.
This talk will cover the final result of GERDA on the search for $^{76}$Ge 0$\nu\beta\beta$ decay, as well as new results on the $^{76}$Ge 2$\nu\beta\beta$ decay half-life and limits on exotic decay modes.
