Bound on 3+1 active-sterile neutrino mixing from the first four-week science run of KATRIN

TL;DR

This paper reports on the KATRIN experiment's first four-week data analysis, setting new limits on light sterile neutrino mass and mixing, improving previous bounds, and constraining anomalies in neutrino physics.

Contribution

First four-week KATRIN data analysis providing new bounds on sterile neutrino parameters, surpassing previous experiments and constraining existing neutrino anomalies.

Findings

No significant spectral distortion observed.

New exclusion bounds on sterile neutrino mass and mixing.

Improved constraints on reactor and gallium anomalies.

Abstract

We report on the light sterile neutrino search from the first four-week science run of the KATRIN experiment in~2019. Beta-decay electrons from a high-purity gaseous molecular tritium source are analyzed by a high-resolution MAC-E filter down to 40 eV below the endpoint at 18.57 keV. We consider the framework with three active neutrinos and one sterile neutrino of mass $m_{4}$. The analysis is sensitive to a fourth mass state $m^2_{4} \lesssim$ 1000 eV$^2$ and to active-to-sterile neutrino mixing down to $|U_{e4}|^2 \gtrsim 2\cdot10^{-2}$. No significant spectral distortion is observed and exclusion bounds on the sterile mass and mixing are reported. These new limits supersede the Mainz results and improve the Troitsk bound for $m^2_{4} <$ 30 eV$^2$. The reactor and gallium anomalies are constrained for $ 100 < \Delta{m}^2_{41} < 1000$ eV$^2$.