An improved upper limit on the neutrino mass from a direct kinematic method by KATRIN

TL;DR

The KATRIN experiment's initial four-week run set a new upper limit of 1.1 eV on the neutrino mass, nearly doubling the sensitivity of previous direct measurements and aiding cosmological research.

Contribution

First four-week KATRIN data provides the most stringent direct upper limit on neutrino mass to date, improving previous bounds significantly.

Findings

Upper limit of 1.1 eV on neutrino mass at 90% confidence level

Effective neutrino mass squared measured as -1.0^{+0.9}_{-1.1} eV^2

Results match KATRIN's sensitivity goal

Abstract

We report on the neutrino mass measurement result from the first four-week science run of the Karlsruhe Tritium Neutrino experiment KATRIN in spring 2019. Beta-decay electrons from a high-purity gaseous molecular tritium source are energy analyzed by a high-resolution MAC-E filter. A fit of the integrated electron spectrum over a narrow interval around the kinematic endpoint at 18.57 keV gives an effective neutrino mass square value of $(-1.0^{+0.9}_{-1.1})$ eV$^2$. From this we derive an upper limit of 1.1 eV (90$\%$ confidence level) on the absolute mass scale of neutrinos. This value coincides with the KATRIN sensitivity. It improves upon previous mass limits from kinematic measurements by almost a factor of two and provides model-independent input to cosmological studies of structure formation.