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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, $m_ν$, from the second physics run of the Karlsruhe Tritium Neutrino experiment. In this experiment, $m_ν$ is probed via a high-precision measurement of the tritium β-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 $m_v$ of ${\\text{0.7eV}c^{-2}}$ at a 90% confidence level (CL). The best fit to the spectral data yields $m\\frac{2}{v}=\\text{(0.26 ± 0.34)eV}^2c^{-4}$, resulting in an upper limit of $m_v{\\text{<0.9eV}}c^{-2}$at 90% CL. By combining this result with the first neutrino-mass campaign, we find an upper limit of mν$m_v{\\text{<0.8eV}}c^{-2}$ at 90% CL.

The KArlsruhe TRItium Neutrino experiment (KATRIN) aims to determine the effective electron (anti)-neutrino mass with a sensitivity of 0.2eV/c \\(^2\\) by precisely measuring the endpoint region of the tritium \\(\\beta \\) -decay spectrum. It uses a tandem of electrostatic spectrometers working as magnetic adiabatic collimation combined with an electrostatic (MAC-E) filters. In the space between the pre-spectrometer and the main spectrometer, creating a Penning trap is unavoidable when the superconducting magnet between the two spectrometers, biased at their respective nominal potentials, is energized. The electrons accumulated in this trap can lead to discharges, which create additional background electrons and endanger the spectrometer and detector section downstream. To counteract this problem, “electron catchers” were installed in the beamline inside the magnet bore between the two spectrometers. These catchers can be moved across the magnetic-flux tube and intercept on a sub-ms time scale the stored electrons along their magnetron motion paths. In this paper, we report on the design and the successful commissioning of the electron catchers and present results on their efficiency in reducing the experimental background.

The long-term energy stability of the 7.5 keV and 17.8 keV conversion electrons of the 9.4 keV and 32 keV neutral transitions respectively in 83m Kr, emitted by solid 83 Rb/ 83m Kr sources, prepared by evaporation in a vacuum, is investigated using two different spectrometers. The results obtained indicate the principal applicability of these 83 Rb sources for monitoring the stability of the energy scale of electron spectrometers in the 20 keV region at the level of ±60 meV for at least two months, which corresponds to the requirement of the new KATRIN tritium neutrino project. Investigations are being continued using sources produced by implantation of 83 Rb ions into different substrates.