From MPG Institute for Physics [Max-Planck-Institut für Physik](DE): “Search for sterile neutrinos- It’s all about a bend in the curve”

From From MPG Institute for Physics [Max-Planck-Institut für Physik](DE)


Prof. Dr. Susanne Mertens
+49 89 32354-590

Dr. Thierry Lasserre
+49 89 32354-590

There are many questions surrounding the elementary particle neutrino, in particular regarding its mass. Physicists are also interested in whether besides the “classic” neutrinos there are variants such as the so-called sterile neutrinos. The KATRIN experiment has now succeeded in strongly narrowing the search for these elusive particles. The publication appeared recently in the journal Physical Review Letters.

KATRIN experiment aims to measure the mass of the neutrino using a huge device called a spectrometer (interior shown)KIT Karlsruhe Institute of Technology [Karlsruher Institut für Technologie] (DE)

The spectrometer of the KATRIN experiment, set to measure the neutrino mass. (Photo: M. Zacher/KIT)

The results of the KATRIN experiment rule out a light sterile neutrino with a mass between 3 and 30 electronvolt. A neutrino within this range would have revealed itself by a bend in the orange line, e.g. as shown here at 10 electronvolt under the final value of 18.6 kiloelectronvolt. (Green line: Spectrum of a virtual light sterile neutrino with a mass of 10 eV; blue line: spectrum of the classical, active neutrino; orange line: combined spectrum. (Plot: KATRIN collaboration)

The area to the left of the lines shows the search ranges of the various experiments for the light sterile neutrino. The area inside the green lines marks the most likely location for light sterile neutrinos. Evaluations of the KATRIN experiment (blue solid line) significantly reduce this search range. (Plot: KATRIN collaboration)

Strictly speaking, the neutrino is not a single particle but rather comprises several species: the electron neutrino, the muon neutrino, and the tau neutrino. These particles are constantly transforming into each other in a process referred to as neutrino oscillation. It is assumed that neutrinos have mass; this is to be determined in the KATRIN experiment, which started in 2019 at the KIT Karlsruhe Institute of Technology [Karlsruher Institut für Technologie] (DE). According to the results to date, the neutrino has a mass less than 1 electron volt.

KATRIN could also be used to track down related species that have so far only been hypothetical: The sterile neutrinos. The heavier branch (mass in kiloelectronvolt range) is considered a candidate for dark matter and will be sought after a new detector is installed in KATRIN. Besides this, there could also a lighter sterile neutrino type.

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The MPG Institute for Physics [Max-Planck-Institut für Physik](DE) (MPP) is a physics institute in Munich, Germany that specializes in high energy physics and astroparticle physics. It is part of the Max-Planck-Gesellschaft and is also known as the Werner Heisenberg Institute, after its first director in its current location.

The founding of the institute traces back to 1914, as an idea from Fritz Haber, Walther Nernst, Max Planck, Emil Warburg, Heinrich Rubens. On October 1, 1917, the institute was officially founded in Berlin as Kaiser-Wilhelm-Institut für Physik (KWIP, Kaiser Wilhelm Institute for Physics) with Albert Einstein as the first head director. In October 1922, Max von Laue succeeded Einstein as managing director. Einstein gave up his position as a director of the institute in April 1933. The Institute took part in the German nuclear weapon project from 1939-1942.

In June 1942, Werner Heisenberg took over as managing director. A year after the end of fighting in Europe in World War II, the institute was moved to Göttingen and renamed the MPG for Physics, with Heisenberg continuing as managing director. In 1946, Carl Friedrich von Weizsäcker and Karl Wirtz joined the faculty as the directors for theoretical and experimental physics, respectively.

In 1955 the institute made the decision to move to Munich, and soon after began construction of its current building, designed by Sep Ruf. The institute moved into its current location on September 1, 1958 and took on the new name the Max Planck Institute for Physics and Astrophysics, still with Heisenberg as the managing director. In 1991, the institute was split into the Max Planck Institute for Physics, the MPG Institute for Astrophysics [Max-Planck-Institut für Astrophysik] (DE) and the MPG Institute for extraterrestrial Physics[MPG Institut für extraterrestrische Physik] (DE).