Tulio Kuhn First direct neutrino-mass measurement with sub-eV sensitivity M. Aker, A. Beglarian, J. Behrens, A. Berlev, U. Besserer, B. Bieringer, F. Block, B. Bornschein et al. Hide abstract | Show figures | Show BibTeX | Show discussion | View PDF | 2105.08533v1 We report the results of the second measurement campaign of the Karlsruhe Tritium Neutrino (KATRIN) experiment. KATRIN probes the effective electron anti-neutrino mass, mν, via a high-precision measurement of the tritium β-decay spectrum close to its endpoint at 18.6keV. In the second physics run presented here, the source activity was increased by a factor of 3.8 and the background was reduced by 25% with respect to the first campaign. A sensitivity on mν of 0.7eV/c2 at 90% confidence level (CL) was reached. This is the first sub-eV sensitivity from a direct neutrino-mass experiment. The best fit to the spectral data yields m2ν=(0.26±0.34)eV4/c4, resulting in an upper limit of m_{\nu}<0.9\,\mathrm{eV/c^2} (90% CL). By combining this result with the first neutrino mass campaign, we find an upper limit of m_{\nu}<0.8\,\mathrm{eV/c^2} (90% CL). Authors' comments: 19 pages, 10 figures, 5 tables