Observables of the Electrical Potential of the KATRIN Tritium Source from Calibration with a High-Intensity Krypton-83m Source

The KArlsruhe TRItium Neutrino experiment currently provides the best neutrino-mass upper limit of 0.8 eV/c2 (90 % C.L.) in the field of direct neutrino-mass measurements. After a total measurement time of 1000 days in 2025, a final sensitivity better than 0.3 eV/c2 (90 % C.L.) is expected, which at the same time requires a detailed study of systematic measurement uncertainties.

One major uncertainty is linked to the electric potential inside the tritium source. Inhomogeneities of the potential lead to a distortion of the β-spectrum, which needs to be characterized in order to reduce the systematic bias in the neutrino-mass measurement.

To this end we use conversion electrons from 83mKr as nuclear standard. Traces of gaseous 83mKr are circulated alongside tritium in the 10 m long source, such that inhomogeneities of the potential are observable as a broadening of the selected mono-energetic 83mKr lines. In this talk we describe the results of 83mKr campaigns carried out in 2021 and 2023 and their impact on the neutrino-mass determination.

This work is supported by the Helmholtz Association and by the Ministry for Education and Research BMBF (grant numbers 05A23PMA, 05A23PX2, 05A23VK2, and 05A23WO6).