Improved eV-scale Sterile-Neutrino Constraints from the Second KATRIN Measurement Campaign

Understand

We present the results of the light sterile neutrino search from the second KATRIN measurement campaign in 2019.

• Approaching nominal activity, $3.76 \times 10^6$ tritium $\beta$-electrons are analyzed in an energy window extending down to $40\,$eV below the tritium endpoint at $E_0 = 18.57\,$keV.
• We consider the $3\nu+1$ framework with three active and one sterile neutrino flavor.
• The analysis is sensitive to a fourth mass eigenstate $m_4^2\lesssim1600\,$eV$^2$ and active-to-sterile mixing $|U_{e4}|^2 \gtrsim 6 \times 10^{-3}$.