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Neutrinos are elementary particles within the Standard Model. The weakness of their interaction with other particles meant that for a long time they remained undetected. Wolfgang Pauli first postulated the existence of the neutrino in 1930 to explain the missing energy in radioactive “beta-minus” decay of atomic nuclei. However, it took almost 30 more years before the neutrino was actually detected.
Neutrinos are released in reactions mediated by the weak interaction, such as nuclear decay, as well as, conversely, in nuclear fusion, such as in the Sun. On Earth, neutrinos are produced by the decay of heavy elements in nuclear reactors. In addition, neutrinos are “messengers” of cosmic events. They provide scientists with the opportunity to study, for instance, supernova explosions, which release most of their energy in a shock wave of neutrinos.
Scientists know about three neutrino “flavors”: the electron neutrino, the muon neutrino, and the tau neutrino. A special feature of the particles, demonstrated in 2002, is their ability to oscillate between flavors.
Despite this, two key questions about the properties of neutrinos remain unanswered: What is the mass of the neutrino, and are neutrinos their own antiparticles?
At the Max Planck Institute for Physics, two groups are investigating these neutrino properties. LEGEND focuses on the question of whether the neutrino is its own antiparticle. Scientists working on the KATRIN experiment are attempting to narrow down the mass of the electron neutrino.
The KATRIN experiment in Karlsruhe is intended to further narrow down the mass of the neutrino. To date, only upper limits on the neutrino mass have been identified. Physicists are now hoping to directly determine the mass of the electron antineutrino. This would also lead to a better understanding of the neutrino mass hierarchy. TRISTAN, which will explicitly search for sterile neutrinos, is a planned continuation of the Katrin experiment.
LEGEND, like the preceding GERDA experiment, is searching for the existence of neutrinoless double beta decay, the existence of which would prove that neutrinos are their own antiparticles. Proof of this would help explain why much more matter than antimatter exists in the universe. The experiment in its first phase is located in the LNGS underground laboratory in the Gran Sasso mountain range in Italy.