Sterile-neutrino search based on 259 days of KATRIN data
- H. Acharya
- M. Aker
- D. Batzler
- A. Beglarian
- J. Beisenkötter
- M. Biassoni
- B. Bieringer
- Y. Biondi
- M. Böttcher
- B. Bornschein
- L. Bornschein
- M. Carminati
- A. Chatrabhuti
- S. Chilingaryan
- D. Díaz Barrero
- B. A. Daniel
- M. Descher
- O. Dragoun
- G. Drexlin
- F. Edzards
- K. Eitel
- E. Ellinger
- R. Engel
- S. Enomoto
- L. Fallböhmer
- A. Felden
- C. Fengler
- C. Fiorini
- J. A. Formaggio
- C. Forstner
- F. M. Fränkle
- G. Gagliardi
- K. Gauda
- A. S. Gavin
- W. Gil
- F. Glück
- R. Grössle
- T. Höhn
- K. Habib
- V. Hannen
- L. Haßelmann
- K. Helbing
- H. Henke
- S. Heyns
- R. Hiller
- D. Hillesheimer
- D. Hinz
- A. Jansen
- C. Köhler
- K. Khosonthongkee
2025-12-03
Neutrinos are the most abundant fundamental matter particles in the Universe and play a crucial part in particle physics and cosmology. Neutrino oscillation, discovered about 25 years ago, shows that the three known species mix with each other. Anomalous results from reactor and radioactive-source experiments 1 suggest a possible fourth neutrino state, the sterile neutrino, which does not interact through the weak force. The Karlsruhe Tritium Neutrino (KATRIN) experiment 2 , primarily designed to measure the neutrino mass using tritium β-decay, also searches for sterile neutrinos suggested by these anomalies. A sterile-neutrino signal would appear as a distortion in the β-decay energy spectrum, characterized by a discontinuity in curvature (kink) related to the sterile-neutrino mass. This signature, which depends only on the shape of the spectrum rather than its absolute normalization, offers a robust, complementary approach to reactor experiments. Here we report the analysis of the energy spectrum of 36 million tritium β-decay electrons recorded in 259 measurement days within the last 40 eV below the endpoint. The results exclude a substantial part of the parameter space suggested by the gallium anomaly and challenge the Neutrino-4 claim. Together with other neutrino-disappearance experiments, KATRIN probes sterile-to-active mass splittings from a fraction of an eV 2 to several hundred eV 2 , excluding light sterile neutrinos with mixing angles above a few per cent.