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

Abstract

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 $m_4^2\lesssim 1600$eV${}^2$ and active-to-sterile mixing $|U_{e4}{|}^2\gtrsim 6\times 10^{-3}$. 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.

14 pages, 8 figures, 2 tables

References in corpus (6)

• The Reactor Antineutrino Anomaly
• Measurement of the solar neutrino capture rate with gallium metal. III: Results for the 2002--2007 data-taking period
• Testing the statistical compatibility of independent data sets
• Focal-plane detector system for the KATRIN experiment
• Detecting sterile neutrinos with KATRIN like experiments
• Bound on 3+1 active-sterile neutrino mixing from the first four-week science run of KATRIN

Cited by in corpus (1)

• Large Extra Dimensions and neutrino experiments