Light, but powerful: Less than 100 years ago, physicists suspected the existence of so-called neutrinos. But these elementary particles can hardly be measured. Now, weight researchers have gone a step further.
Karlsruhe – An international team of researchers has achieved success in particle physics with the help of a huge, tonne balance at the Karlsruhe Institute of Technology (KIT).
The scientists weighed the lightest known particle in the universe, the neutrino. The unit of measure for this is not grams, but electron volts (eV). With their experiments, the experts were able to determine 0.8 eV as the upper limit for the neutrino mass, as they report in the journal “Nature Physics”. This broke through the so-called 1 eV barrier. Experts celebrate this as a great success.
Neutrinos are electrically neutral elementary particles and may have played an important role in the formation of the universe. Among other things, they are released during nuclear fusions in the sun and play a role in the radioactive decay of atomic nuclei and supernova explosions in space. In addition, they are everywhere, they are the most common elementary particles in the universe: billions of them stream through just one finger every second. Because they hardly interact with their environment, you don’t notice anything. Even planets like Earth don’t stop neutrinos.
Up until now, devices to study neutrinos have been lacking
This makes it difficult to capture them. In 1930, the Austrian Nobel Prize winner Wolfgang Pauli postulated the existence of particles for the first time. The background was that during the decay of atomic nuclei, measurement data for neutrons and electrons did not fit the principle of energy conservation in physics – something that was often missing.
The neutrinos were not detected until more than two decades later and were even considered massless for a long time. Because of inaccurate measuring equipment, it has not been possible to say much more about neutrinos up to now. To a certain extent, they defy scientific observation and are therefore also called “ghost particles”.
This is where the Karlsruhe Tritium Neutrino Experiment, or “Katrin” for short, comes in: In the 70 meter long facility, the energy distribution during the decay of tritium is measured in a vacuum. This is an unstable isotope of hydrogen. The mass of the neutrinos can be determined from the values. “Katrin” was put into operation in 2019. Over time, the researchers made the instruments more and more precise. The KIT speaks of the most accurate scales in the world. In addition, every influence on the neutrino mass had to be examined in detail in order to rule out interfering effects on the result.
Measurements of the neutrino mass are to be refined by 2025
“The particle physics community is excited that Katrin has broken the 1 eV barrier,” KIT quoted the participating neutrino expert John Wilkerson from the University of North Carolina as saying in a statement. The measurements of the neutrino mass at KIT are to be refined by the end of 2024, it was said. A new detector system should then help in the search for so-called sterile neutrinos from 2025. dpa
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