KATRIN weighs neutrinos more precisely than ever

New measurements from a large-scale experiment at the Karlsruhe Institute of Technology (KIT) published in the journal Science / Christian Weinheimer from the Institute for Nuclear Physics involved

Neutrinos are among the most enigmatic particles in the universe. They are all’around us and yet they rarely interact with matter. In cosmology, they influence the formation of structures of galactic scale, while in particle physics they serve as indicators of previously unknown physical processes due to their minuscule mass. The exact measurement of neutrino mass is therefore essential for fully understanding the fundamental laws of nature. In this context, the international ’Karlsruhe Tritium Neutrino Experiment’ (KATRIN) at the Karlsruhe Institute of Technology (KIT), in which the astroparticle physicist Prof Christian Weinheimer’s research group from the University of Münster is also involved, has set a new benchmark. Based on data published in the journal Science, researchers were able to deduce that neutrinos weigh a maximum of 8 x 10^-37 kilograms (this corresponds to 0.45 eV/c2 in the unit commonly used in physics). No one has ever been able to determine the mass so precisely before.

Christian Weinheimer is one of the founding researchers of KATRIN and served as one of two spokespersons for the experiment until 2022. ’We are proud that our KATRIN collaboration has succeeded in significantly improving the upper limit for the neutrino mass with important contributions,’ he stated. This achievement was made possible not only by collecting more data, but also by significantly reducing the rate of background interference and systematic uncertainties.

The Münster team of physicists, engineers and technicians have long been significantly involved in the development and operation of KATRIN. The analysis and measurement methods developed in Münster significantly improve the sensitivity of the experiments. Among other things, the group collaborated with the workshops of the Institute of Nuclear Physics to design specialised scientific instruments such as various high-precision electron calibration sources, precision high-voltage and the wire electrode system in the giant KATRIN spectrometer.

Scientists from more than 20 institutions from seven countries are working on KATRIN. The experiment makes use of the beta decay of tritium, an unstable hydrogen isotope; the energy distribution of the resulting electrons allows researchers to directly measure the neutrino mass. Sophisticated technical components are required to achieve this: The 70-metre-long experiment houses an intense tritium source and a high-resolution spectrometer with a 10-metre diameter. This technology has resulted in unrivalled precision. The neutrino mass measurements will continue until the end of 2025. After that, researchers will begin installing a new detector system for the search of so-called sterile neutrinos and develop concepts for next-generation experiments.

Original publication

Aker M. et al. (2025): Direct neutrino-mass measurement based on 259 days of KATRIN data. Science; adq9592