A scientist works on the germanium detector array in the clean room of Gran Sasso underground laboratory.
Working on the germanium detector array in the clean room of Gran Sasso underground laboratory.
Image: J. Suvorov / GERDA
  • Research news
  • Reading time: 3 MIN

Major steps forward in understanding neutrino propertiesClosing in on elusive particles

In the quest to prove that matter can be produced without antimatter, the GERDA experiment at the Gran Sasso Underground Laboratory is looking for signs of neutrinoless double beta decay. The experiment has the greatest sensitivity worldwide for detecting the decay in question. To further improve the chances of success, a follow-up project, LEGEND, uses an even more refined decay experiment.

While the Standard Model of Particle Physics has remained mostly unchanged since its initial conception, experimental observations for neutrinos have forced the neutrino part of the theory to be reconsidered in its entirety.

Neutrino oscillation was the first observation inconsistent with the predictions and proves that neutrinos have non-zero masses, a property that contradicts the Standard Model. In 2015, this discovery was rewarded with the Nobel Prize.

Are neutrinos their own antiparticles?

Additionally, there is the longstanding conjecture that neutrinos are so-called Majorana particles: Unlike all other constituents of matter, neutrinos might be their own antiparticles. This would also help explain why there is so much more matter than antimatter in the Universe.

The GERDA experiment is designed to scrutinize the Majorana hypothesis by searching for the neutrinoless double beta decay of the germanium isotope 76Ge: Two neutrons inside a 76Ge nucleus simultaneously transform into two protons with the emission of two electrons. This decay is forbidden in the Standard Model because the two antineutrinos – the balancing antimatter – are missing.

The Technical University of Munich (TUM) has been a key partner of the GERDA project (GERmanium Detector Array) for many years. Prof. Stefan Schönert, who heads the TUM research group, is the speaker of the new LEGEND project.

The GERDA experiment achieves extreme levels of sensitivity

GERDA is the first experiment to reach exceptionally low levels of background noise and has now surpassed the half-life sensitivity for decay of 1026 years. In other words: GERDA proves that the process has a half-life of at least 1026 years, or 10,000,000,000,000,000 times the age of the Universe.

Physicists know that neutrinos are at least 100,000 times lighter than electrons, the next heaviest particles. What mass they have exactly, however, is still unknown and another important research topic.

In the standard interpretation, the half-life of the neutrinoless double beta decay is related to a special variant of the neutrino mass called the Majorana mass. Based the new GERDA limit and those from other experiments, this mass must be at least a million times smaller than that of an electron, or in the terms of physicists, less than 0.07 to 0.16 eV/c2 [1].

Consistent with other experiments

Also other experiments limit the neutrino mass: the Planck mission provides a limit on another variant of the neutrino mass: The sum of the masses of all known neutrino types is less than 0.12 to 0.66 eV/c2.

The tritium decay experiment KATRIN at the Karlsruhe Institute of Technology (KIT) is set-up to measure the neutrino mass with a sensitivity of about 0.2 eV/c2 in the coming years. These masses are not directly comparable, but they provide a cross check on the paradigm that neutrinos are Majorana particles. So far, no discrepancy has been observed.


During the reported data collection period, GERDA operated detectors with a total mass of 35.6 kg of 76Ge. Now, a newly formed international collaboration, LEGEND, will increase this mass to 200 kg of 76Ge until 2021 and further reduce the background noise. The aim is to achieve a sensitivity of 1027 years within the next five years.


The GERDA collaboration: Probing Majorana neutrinos with double beta decay
Science, published online on Thursday 5 September, 2019 – DOI: 10.1126/science/ aav8613

More information:

GERDA is an international European collaboration of more than 100 physicists from Belgium, Germany, Italy, Russia, Poland and Switzerland. In Germany, GERDA is supported by the Technical Universities of Munich and Dresden, the University of Tübingen and the Max Planck Institutes for Physics and for Nuclear Physics. German funding is provided by the German Federal Ministry of Education and Research (BMBF), the German Research Foundation (DFG) via the Excellence Cluster Universe and SFB1258, as well as the Max Planck Society.

Prof. Schönert received an ERC Advanced Grant for preparatory work on the LEGEND project in 2018. A few days ago, Prof. Susanne Mertens received an ERC grant for her work on the KATRIN experiment. In the context of that experiment, she will search for so-called sterile neutrinos.

[1] In particle physics masses are specified not in kilograms, but rather in accordance with Einstein’s equation E=mc2: electron volts [eV] divided by the speed of light squared. Electron volts are a measure of energy. This convention is used to circumvent unfathomably small units of mass: 1 eV/c2 corresponds to 1.8 × 10-36 kilograms.

High resolution images

Technical University of Munich

Corporate Communications Center Petra Riedel / Andreas Battenberg

Contacts to this article:

Prof. Dr. Stefan Schönert
Technical University of Munich
Experimental Astroparticlephysics (E15)
Tel.: +49 89 289 12511
E-Mail: schoenert(at)ph.tum.de

Article at tum.de

 Mit dem Borexino-Detektor ist es einem Physik-Team gelungen, Neutrinos aus den beiden Fusions-Zyklen der Sonne nachzuweisen.

Sun model completely confirmed for the first time

The Borexino experiment research team has succeeded in detecting neutrinos from the sun's second fusion process, the Carbon Nitrogen Oxygen cycle (CNO cycle) for the first time. This means that all of the theoretical...

A view inside the KATRIN experiment.

More accurate than expected

Despite their extremely small mass, neutrinos play a key role in cosmology and particle physics. After evaluation of the first measurement results in the Karlsruhe Tritium Neutrino Experiment (KATRIN), it is now clear: The...

As part of her project, Dr. Barbara Lechner observes catalytic processes at atomic level. The green and orange peaks represent platinum clusters each containing 20 atoms on a flat iron oxide surface. This project, along with six others, is to receive funding from ERC Starting Grants.

EU funding for top-level research at TUM

The European Research Council (ERC) has announced that seven of its prestigious ERC Starting Grants will be awarded to scientists at the Technical University of Munich (TUM) this year. The subject matter of the projects...

Der Helixnebel, 700 Lichtjahre von der Erde entfernt. Der Cluster ORIGINS erforscht die Entstehung des Universums und des ersten Lebens. (Bild: ESO/VISTA/J. Emerson)

TUM successfully presents four research Clusters of Excellence

The Technical University of Munich (TUM) has got off to another successful start in the extremely competitive Excellence Initiative organized by Germany’s government and federal states. Over the next seven years, four...

Das IceCube Lab am Südpol unter den Sternen.

First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by Prof. Elisa Resconi from the Technical University of Munich (TUM), provides an important piece of...

Simulation der Kollision von Blei-Ionen bei ALICE.

The symmetry of the universe

Our existence is still a great mystery in theoretical physics. Why did anti-matter disappear almost completely from our universe, whereas matter did not? Scientists are attempting to solve this mystery at the particle...