Giuseppe Salamanna: “The quest for LFV through Neutrinoless double-beta decay in Germanium: LEGEND”


If neutrinos were the one (and only) instance of elementary particles of the Majorana type, they could undergo a hypothetical process violating lepton number, the Neutrinoless double-beta decay (0νββ). If 0νββ indeed happened, it would be enough to claim the Majorana nature of neutrinos.
Several experiments have been conceived to search for 0νββ in a handful of isotopes baring a specific energy-momentum configuration. A variety of experimental techniques are being employed in the quest. So far the best lower limit on the half-life for 0νββ decay is of around 10^{​​26}​​ yr and it comes from an experiment called GERDA, based at the Italian underground Gran Sasso Lab. GERDA used around 40 kg of $^76$Ge both as source and as semi-conducting detector.
In this seminar I will focus on the next generation experiment, LEGEND, which will take the baton from GERDA and its US counterpart (MAJORANA DEMONSTRATOR).
Using a two-stage approach with about 200 kg and then 1 ton of germanium, LEGEND aims to attain a sensitivity around $10^{​​28}​​$ yr in half-life, probing the standard inverted-ordering neutrino mass scenario. I will review the general concept and design of LEGEND; describe the detectors and their preliminary performance. I will also illustrate how the backgrounds can have a dramatic effect on the search; and in which way it can be mitigated, with a particular stress on the liquid-argon based active veto. Finally, I will provide an expected timeline, starting from LEGEND-200 and its installation due to start this spring despite COVID.