KATRIN Experiment Significantly Limits Possibility of ‘Sterile‘ Neutrino
Karlsruhe, Germany – December 4, 2025 – A new analysis of data from the Karlsruhe Tritium Neutrino experiment (KATRIN) has dramatically reduced the potential mass range for sterile neutrinos, hypothetical particles proposed to explain anomalies in previous neutrino experiments. The results, published today in Nature, exclude the existence of sterile neutrinos with masses between one and several hundred electron volts.
For years, physicists have investigated the possibility of a fourth type of neutrino – a “sterile” neutrino that interacts with matter only through gravity, unlike the three known neutrino flavors. anomalies observed in other experiments hinted at their existence, but the KATRIN collaboration sought to definitively test these claims.
The KATRIN experiment precisely measures the energy spectrum of electrons emitted during the decay of tritium. The presence of sterile neutrinos would manifest as a “kink” or general distortion in this spectrum.Researchers evaluated data from over 36 million electrons detected over 259 days, finding “no meaningful signal from sterile neutrinos,” according to the team.
“We have demonstrated neither a noticeable kink in the energy spectrum of the electrons nor a broader distortion of the spectrum,” the physicists explain. The experiment’s precision – measuring energies with sub-electron volt accuracy and exceptionally low background noise – lends high reliability to the findings.
“The area in which sterile neutrinos could still hide is now significantly smaller – and the probability of the existence of this fourth type of neutrino has decreased significantly,” stated Thierry Lasserre from the Max Planck Institute for Nuclear Physics in Heidelberg.
KATRIN is set to complete data collection in 2025, aiming to analyze data from more than 220 million electrons – a six-fold increase in statistics. A planned upgrade in 2026, adding a new detector, will extend KATRIN’s reach to search for sterile neutrinos with masses in the kiloelectronvolt range, potentially linking them to the search for dark matter.
(Nature, 2025; doi: 10.1038/s41586-025-09739-9)