Their mass is extremely low, but how light are neutrinos really? A collaboration comprising German and international research groups has optimized its experiments to determine the mass of these “ghost particles.” In doing so, they succeeded in further adjusting downward the upper limit on the neutrino mass scale that had previously been determined in similar experiments. The study is published in the journal Physical Review Letters.

As part of the “Electron Capture in Ho-163 Experiment” (ECHo), the researchers are using the isotope Holmium-163 (Ho-163), whose decay processes allow for conclusions on the neutrino mass. According to ECHo spokesperson Prof. Dr. Loredana Gastaldo, a scientist at Heidelberg University’s Kirchhoff Institute for Physics, the current results verify that even larger-scale investigations will be feasible in future to get even closer to the mass of neutrinos and ultimately precisely determine it.

Neutrinos are elementary particles with extremely low mass that have no electrical charge. Because their interaction with matter is very weak, the properties of these “ghost particles” are very difficult to determine. This is especially true for the neutrino mass, which has yet to be precisely measured, with only its upper limit being known. According to Gastaldo, determining the mass could pave the way for new theoretical models beyond the standard model of particle physics and thereby contribute to a better understanding of the evolution of our universe.