GERDA detector: Neutrino physics
Are neutrinos really their own antiparticles? Why are they so light and what mass do they have? Scientists working on the GERDA experiment want to find out more about the properties of neutrinos.
Neutrinos are some of the most common particles in the universe. They are produced, for example, in the nuclear fusion taking place in the interior of stars, as well as in the Sun and during nuclear fission in power plants. Since they interact only via the weak force, they are extremely difficult to detect.
According to the present state of our knowledge, every known particle has an antiparticle with the opposite electric charge: anti-quarks, or anti-leptons (positron, anti-muon and anti-tau). As the neutrino is electrically neutral, it could be the odd one out here and be its own antiparticle. If the experiment can confirm this assumption, the researchers will have new starting points for gaining a better understanding of the physics of the universe.
The GERDA experiment
The GERDA experiment is investigating whether the neutrino is its own antiparticle. The search is on for so-called neutrinoless double-beta decay, which has never been observed before. One isotope which could exhibit this extremely rare radioactive decay is germanium-76. The experiment is therefore based on germanium detectors which have been enriched with this isotope.
Neutrinoless double-beta decay involves the conversion of two neutrons into two protons and two electrons. Two neutrinos are also released in this process, but they can annihilate each other – provided they are their own antiparticles. This decay therefore exists only if
- neutrinos and their antiparticles are identical
- and have a mass.
The GERDA experiment incorporates a total of 36 kilograms of detector material. This corresponds to around 1026 germanium-76 nuclei in total. With this number of nuclei, it should prove possible to detect this decay within a few years if its half-life is 1026 years or less.
Should GERDA measure a small number of the hypothetical and extremely rare decays, this would be a possible answer to the question: Why the universe contains matter, but no longer contains any antimatter – the key to our existence. Moreover, the physicists could draw conclusions about the mass of the neutrino.
Underground environment with extremely low radiation
As neutrinoless double-beta decay is so rare, the GERDA experiment has to have the best possible protection against disturbing influences. It is therefore located in the Gran Sasso underground laboratory in Italy, where 1.4 kilometers of mountain rock shield it against cosmic radiation from space.
The germanium detectors are furthermore in an extremely clean environment: in a tank made of specially selected steel with a very low radiation rate which is filled with liquid argon. This vessel is in turn housed in a ten-meter-diameter tank filled with ultrapure water.
The GERDA collaboration has around 120 members from 16 institutes in six European countries, including the Max Planck Institutes for Physics (MPP) and Nuclear Physics. The GERDA Group at the MPP was responsible for constructing the cleanroom above the cryostat, and for developing and constructing the infrastructure used to lower the detectors into the argon tank, the so-called lock system.
Further information on the GERDA group
Fellow at the MPP
Events and meetings
Production, characterization and operation of 76Ge enriched BEGe detectors in GERDA
EPJC 75 (2015) 39
Results on Neutrinoless Double-β Decay of 76Ge from Phase I of the GERDA Experiment
Phys. Rev. Lett 111 (2013) 122503
Results on ββ decay with emission of two neutrinos or Majorons in 76Ge from GERDA Phase I
Eur. Phys. J. C 75 (2015) 416
cover page of EPJC vol 75/9
Pulse shape discrimination for GERDA Phase I data
Eur. Phys. J. C 73 (2013) 2583
The background in the 0νββ experiment GERDA
Eur. Phys. J. C 74 (2014) 2764
The GERDA experiment for the search of 0νββ decay in 76Ge
Eur. Phys. J. C 73 (2013) 2330