Differential spectrum modeling for keV sterile neutrino search at KATRIN

Starting in 2026, the KATRIN experiment will conduct a high-statistics measurement of the differential tritium β-spectrum to energies deep below the kinematic endpoint. This enables the search for keV sterile neutrinos with masses m4 ≤ 18 keV, aiming for a statistical sensitivity of |Ue4|2=sin2θ∼ 10−6. The differential spectrum is obtained by decreasing the retarding potential of KATRIN’s main spectrometer, and by determining the β-electron energies by their energy deposition in the new TRISTAN SDD array. In this mode of operation, the existing integral model of the tritium spectrum is insufficient, and a novel differential model is developed. So far, the model includes 20 systematics and can perform comprehensive sensitivity studies. The gained insights are employed to find the optimal beamline configuration for the measurement and to investigate potential hardware upgrades that significantly improve the sensitivity. This talk provides a summary of the systematics, the model approach, and shows how the impact of several dominant systematics can be reduced.
This work is supported by the Helmholtz Association and by the Ministry for Education and Research BMBF (grant numbers 05A23PMA, 05A23PX2, 05A23VK2, and 05A23WO6).