The LEGEND collaboration wants to build a next-generation germanium-based experiment to search for neutrinoless double beta decay. It was formed as a follow-up to the GERDA and MAJORANA collaborations. The GERDA experiment is operated with about 40 kg of Germanium. LEGEND will have a first phase with 200 kg of Germanium installed in the GERDA cryostat in the Gran Sasso underground laboratory. The final goal is to build an experiment based on one ton of germanium with a new infrastructure.
Neutrinoless double-beta decay is only possible if neutrinos are their own antiparticle. Whether they are or not is not known, even though neutrinos are a fundamental ingredient for nuclear fission, nuclear fusion and the evolution of the universe and, thus, well researched. If they are their own antiparticle, this also contributes to one possible explanation for the disappearance of antimatter.
Neutrinoless double-beta decay is, even if it exists, an extremely rare phenomenon. Observing it is impossible in the presence of the normal level of natural radioactivity, which creates background events, i.e. events that look like signal events but are not. Therefore, experiments searching for neutrinoless double-beta decay have to be extremely well shielded against radioactive background originating from surrounding materials and against cosmic radiation.
In order to minimize the influence of penetrating cosmic radiation, the experiments must be conducted very deep underground. The two laboratories SNOLAB in Canada and CJPL are the deepest in the world and both are well suited. In addition, all parts used to build the experiment itself have to be made of specially selected materials which contain as little radioactivity as possible. The overall background level has to be reduced by at least one order of magnitude compared to the GERDA and MAJORANA experiments.
To realize the LEGEND project, scientists at the MPI for Physics have initiated three subprojects.
The goal is to design improved detectors in which background can be better identified.
The goal is to study cosmic-muon-induced neutrons which cause an especially dangerous background.
The goal is to provide an active veto against radioactive background and at the same time hold and protect the germanium detectors.
Alpha-event and surface characterisation in segmented true-coaxial HPGe detectors
Nucl. Instrum. Meth. A 858 (2017) 80-89
The GALATEA test-facility for high purity germanium detectors
Nucl.Instrum.Meth. A 782 (2015) 56
Measurement of the temperature dependence of pulse lengths in an n-type germanium detector
Eur. Phys. J. Appl. Phys. 56 (2011) 10104
Pulse shape simulation for segmented true-coaxial HPGe detectors
Eur. Phys. J. C 68, 609-618 (2010)
Neutron Interactions as Seen by A Segmented Germanium Detector
Eur. Phys. J. A 36, 139-149 (2008)
Characterization of the first true coaxial 18-fold segmented n-type prototype detector for the GERDA project Nucl.Instrum.Meth. A 577 (2007) 574
A TV program called “nano” on the 3sat channel reports on the deepest underground laboratory in the world: Jinping in Sichuan, China. Deep under the mountain, screened from cosmic radiation, germanium detectors are used in the search for traces of dark matter.
Watch the report from October 20, 2014 in the 3sat mediatheque (in German, video time 06:18 -12:30)