First neutrino mass measurement with the KATRIN experiment

The KATRIN (Karlsruhe Tritium Neutrino) experiment is designed to determine the effective mass of the electron anti-neutrino with an unprecedented sensitivity of 0.2 eV/c² (90% C.L.) in a direct and model-independent way. Tritium β-decay electrons, emitted in a high-luminosity molecular source, are analyzed with a MAC-E filter. The effective electron anti-neutrino mass squared is inferred from a fit to the integral spectrum in an energy window close the tritium endpoint. In this work, we report on the analysis of the first four-week science run of KATRIN in spring 2019. Considering statistical and systematic uncertainties, we find a central value of the effective electron anti-neutrino mass of ${m}_{v}^{2}=(-{1.0}_{-1.0}^{+0.9}){\text{eV}}^{2}$. Following the method of Lokhov and Tkachov, we derive an upper limit of 1.1 eV at 90% C.L. on the absolute neutrino mass scale.