Direct neutrino-mass measurement with sub-electronvolt sensitivity

Since the discovery of neutrino oscillations, we know that neutrinos have non-zero mass. However, the absolute neutrino-mass scale remains unknown. Here we report the upper limits on effective electron anti-neutrino mass, m(nu), from the second physics run of the Karlsruhe Tritium Neutrino experiment. In this experiment, m(nu) is probed via a high-precision measurement of the tritium beta-decay spectrum close to its endpoint. This method is independent of any cosmological model and does not rely on assumptions whether the neutrino is a Dirac or Majorana particle. By increasing the source activity and reducing the background with respect to the first physics campaign, we reached a sensitivity on m(nu) of 0.7 eV c(-2) at a 90% confidence level (CL). The best fit to the spectral data yields m(nu)(2) = (0.26 +/- 0.34) eV(2) c(-4), resulting in an upper limit of m(nu) < 0.9 eV c(-2) at 90% CL. By combining this result with the first neutrino-mass campaign, we find an upper limit of m(nu) < 0.8 eV c(-2) at 90% CL.

Automated summary

This article reports on the upper limits of the effective electron anti-neutrino mass from the second physics run of the Karlsruhe Tritium Neutrino experiment. Using a high-precision measurement of the tritium beta-decay spectrum, independent of cosmological models and particle assumptions, the sensitivity and upper limit of the neutrino mass were determined.