The Karlsruhe Tritium Neutrino (KATRIN) experiment is the world’s leading project for directly measuring the neutrino mass. Located at the Karlsruhe Institute of Technology, KATRIN uses an intense windowless gaseous tritium source and a high-resolution spectrometer to analyze the energy of β-decay electrons with sub-eV precision. This 70-m-long setup enables the most sensitive laboratory probe of the neutrino mass scale, complementing cosmological experiments. KATRIN’s measurements have already reached a sensitivity of 0.45 eV and continue to improve as a lot of new data (x5) are still to analyzed

Search for Light Sterile Neutrinos

Beyond its main neutrino-mass goal, KATRIN is also uniquely sensitive to additional, “sterile” neutrino states that would not interact via the Standard Model forces. Such particles could explain anomalies observed in reactor and source experiments and would mark physics beyond the Standard Model. Our group at MPIK leads this analysis, which looks for tiny “kinks” in the tritium β-decay spectrum produced by the emission of a sterile neutrino. Our recent publication in Nature set the world’s most stringent direct limits in the eV-mass range, excluding much of the parameter space suggested by earlier hints. You can also see an associated overview of the research in the field discussed in this New York Times article. 

Search for Cosmic Relic Neutrinos

KATRIN also provides a powerful laboratory to probe the cosmic neutrino background, the relic neutrinos that decoupled one second after the Big Bang. These neutrinos could occasionally be captured on tritium, creating a distinctive electron signal just above the β-decay endpoint. Our MPIK group leads this pioneering search, which currently yields the best laboratory limits on the local relic-neutrino overdensity, improved by two orders of magnitude over previous results. Though detection remains a long-term challenge, this work establishes the experimental foundation for future observation of the relic neutrino background.