New Constraint on the Local Relic Neutrino Background Overdensity with the First KATRIN Data Runs

TL;DR

This paper reports on the first search for the cosmic relic neutrino background using KATRIN data, setting new upper limits on local neutrino overdensity and improving previous experimental constraints.

Contribution

First direct search for relic neutrino background with KATRIN, providing new upper limits and updated sensitivity projections.

Findings

No significant relic neutrino overdensity detected.

Set upper limit of 9.7e10 at 90% confidence level.

Projected sensitivity of KATRIN to <1e10 at 90% confidence level.

Abstract

We report on the direct cosmic relic neutrino background search from the first two science runs of the KATRIN experiment in 2019. Beta-decay electrons from a high-purity molecular tritium gas source are analyzed by a high-resolution MAC-E filter around the kinematic endpoint at 18.57 keV. The analysis is sensitive to a local relic neutrino overdensity of 9.7e10 (1.1e11) at a 90% (95%) confidence level. A fit of the integrated electron spectrum over a narrow interval around the kinematic endpoint accounting for relic neutrino captures in the Tritium source reveals no significant overdensity. This work improves the results obtained by the previous kinematic neutrino mass experiments at Los Alamos and Troitsk. We furthermore update the projected final sensitivity of the KATRIN experiment to <1e10 at 90% confidence level, by relying on updated operational conditions.