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 18.6 keV. 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 0.7 eV/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 mν2=(0.26±0.34) eV2/c4, resulting in an upper limit of mν<0.9 eV/c2 (90% CL). By combining this result with the first neutrino mass campaign, we find an upper limit of mν<0.8 eV/c2 (90% CL).
A limit on the electron-neutrino charge radius Irl is derived from a measurement of the weakneutral-current vector coupling constant gv obtained in electron-neutrino electron elastic scattering. The 90%-confidence interval for gv is -0.177 < gv < 0.187, which for sin2ew -0.227 implies that the v, mean-square charge radius is in the range -2.74x < ( r 2 ) < 4.88X cm2, or simply Irl < 2.2x 10-l6 cm. This is the first experimental bound on the v, charge radius, and is the same order of magnitude as bounds for v, structure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.