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05.09.2019 – 20:14

Technische Universität München

The GERDA-Collaboration: Major steps forward in understanding neutrino properties

TECHNICAL UNIVERSITY OF MUNICH

Corporate Communications Center

phone: +49 89 289 10510 - e-mail: presse@tum.de - web: www.tum.de

This text on the web: http://www.tum.de/nc/die-tum/aktuelles/pressemitteilungen/details/35672/

High resolution images: https://mediatum.ub.tum.de/1518985

NEWS RELEASE

Closing in on elusive particles

Major steps forward in understanding neutrino properties

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 76-Ge: Two neutrons inside a 76-Ge 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 10^26 years. In other words: GERDA proves that the process has a half-life of at least 10^26 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/c^2 [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/c^2.

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/c^2 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.

From GERDA to LEGEND

During the reported data collection period, GERDA operated detectors with a total mass of 35.6 kg of 76-Ge. Now, a newly formed international collaboration, LEGEND, will increase this mass to 200 kg of 76-Ge until 2021 and further reduce the background noise. The aim is to achieve a sensitivity of 10^27 years within the next five years.

Publication:

The GERDA collaboration: Probing Majorana neutrinos with double beta decay

Science, published online on Thursday 5 September, 2019

DOI: 10.1126/science/ aav8613

Link: https://science.sciencemag.org/lookup/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=mc^2: 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/c^2 corresponds to 1.8 × 10^-37 kilograms.

Homepage of the GERDA-Collaboration: https://www.mpi-hd.mpg.de/gerda/home.html

High resolution image: https://mediatum.ub.tum.de/1518985

Contact:

Technical University of Munich

Prof. Dr. Stefan Schönert

Tel.: +49 89 289 12511

E-Mail: schoenert@ph.tum.de

Technical University of Dresden

Prof. Dr. Kai Zuber

Tel.: +49 351 463 42250

E-Mail: zuber@physik.tu-dresden.de

University of Tübingen

Prof. Dr. Josef Jochum

Tel.: +49 7071 297 4453

E-Mail: Josef.Jochum@uni-tuebingen.de

Max Planck Institute for Physics, Munich

Prof. Dr. Allen Caldwell

Tel.: +49 89 323 54207

E-Mail: caldwell@mpp.mpg.de

Max Planck Institute for Nuclear Physics, Heidelberg

Prof. Dr. Werner Hoffmann

Tel.: +49 6221 516 330

E-Mail: Werner.Hofmann@mpi-hd.mpg.de

Prof. Dr. Manfred Lindner

Tel.: +49 6221 516 800

E-Mail: lindner@mpi-hd.mpg.de

University of Zürich

Prof. Dr. Laura Baudis

Tel.: +41 44 635 5777

E-Mail: lbaudis@physik.uzh.ch

The Technical University of Munich (TUM) is one of Europe's leading research
universities, with around 550 professors, 41,000 students, and 10,000 academic
and non-academic staff. Its focus areas are the engineering sciences, natural
sciences, life sciences and medicine, combined with economic and social
sciences. TUM acts as an entrepreneurial university that promotes talents and
creates value for society. In that it profits from having strong partners in
science and industry. It is represented worldwide with the TUM Asia campus in
Singapore as well as offices in Beijing, Brussels, Cairo, Mumbai, San Francisco,
and São Paulo. Nobel Prize winners and inventors such as Rudolf Diesel, Carl von
Linde, and Rudolf Mößbauer have done research at TUM. In 2006, 2012 and 2019 it
won recognition as a German "Excellence University." In international rankings,
TUM regularly places among the best universities in Germany. www.tum.de 

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