Analysis of first KATRIN data and searches for keV-scale sterile neutrinos

The phenomenon of neutrino oscillation stands in contradiction with the Standard Model of Particle Physics (SM) where neutrinos are formulated as massless particles. One way to introduce a non-zero neutrino mass to the SM is the so-called see-saw-mechanism. It adds at least one sterile neutrino to the particle framework. A sterile neutrino would not participate in any SM interaction, only interact gravitationally and would be of arbitrary mass-scale. These unique properties make a sterile neutrino an interesting Dark Matter candidate.

The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to determine the effective electron anti-neutrino mass with a sensitvity of $0.2\, \mathrm{eV}/c^{2}$ (90 $\%$ C.L.) by observing the tritium $\beta$-decay close to its kinematic endpoint. Studies show that the experiment can be additionally extended to search for a sterile neutrino, for example on the keV mass-scale.

This thesis specifies how the KATRIN experiment can be operated to search for keV-scale sterile neutrinos without any significant hardware modifications. It presents a first comprehensive overview of all yet known systematic effects that occur in such a measurement. ... mehrThis information is used for a first keV-scale sterile neutrino measurement with KATRIN data.
By analyzing 82 KATRIN $\beta$-spectrum scans wit a total measurement time of approximately 160 hours, the current laboratory limit on the active-to-sterile mixing angle could be improved by up to a factor of eight on a mass scale of $0.10 \, \mathrm{keV} \leq m_{\nu_\mathrm{s}} \leq 0.76 \, \mathrm{keV}$ with a resolution on the mixing amplitude of up to $\sin^2 \theta < 2.33 \cdot 10^{-3}$.