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Journal Article

Improved eV-scale sterile-neutrino constraints from the second KATRIN measurement campaign


Rodejohann,  W.
Werner Rodejohann - ERC Starting Grant, Junior Research Groups, MPI for Nuclear Physics, Max Planck Society;

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Aker, M., Batzler, D., Beglarian, A., Behrens, J., Berlev, A., Besserer, U., et al. (2022). Improved eV-scale sterile-neutrino constraints from the second KATRIN measurement campaign. Physical Review D, 105(7): 072004. doi:10.1103/PhysRevD.105.072004.

Cite as: https://hdl.handle.net/21.11116/0000-000A-E4D3-6
We present the results of the light sterile neutrino search from the second Karlsruhe Tritium Neutrino (KATRIN) measurement campaign in 2019. Approaching nominal activity, 3.76 x 10(6) tritium ss-electrons are analyzed in an energy window extending down to 40 eV below the tritium end point at E-0 = 18.57 keV. We consider the 3 nu + 1 framework with three active and one sterile neutrino flavors. The analysis is sensitive to a fourth mass eigenstate m(4)(2) less than or similar to 1600 eV(2) and active-to-sterile mixing |U-e4|(2) greater than or similar to 6 x 10(-3). As no sterile-neutrino signal was observed, we provide improved exclusion contours on m(4)(2) and |U-e4|(2) at 95% C.L. Our results supersede the limits from the Mainz and Troitsk experiments. Furthermore, we are able to exclude the large Delta m(41)(2) solutions of the reactor antineutrino and gallium anomalies to a great extent. The latter has recently been reaffirmed by the BEST Collaboration and could be explained by a sterile neutrino with large mixing. While the remaining solutions at small Delta m(41)(2) are mostly excluded by short-baseline reactor experiments, KATRIN is the only ongoing laboratory experiment to be sensitive to relevant solutions at large Delta m(41)(2) through a robust spectral shape analysis.