Measurement of High-Energy Muon Neutrinos with the IceCube Neutrino Observatory

More than a century after their discovery the origin of high-energy cosmic rays remains unknown. With the discovery of high-energy astrophysical neutrinos by the IceCube collaboration a new window into the universe has been opened. The discovery relies on high-energy neutrinos which interact within the instrumented volume of the detector. A complementary search strategy is the selection of charged-current muon neutrino events which can interact outside the instrumented volume. Due to the large muon range the effective area is significantly larger, but the field of view is restricted to the Northern Hemisphere. In this thesis the selection of muon neutrino events using ''Boosted Decision Trees`` is presented. In total more than 350,000 neutrino candidates have been selected using data from 2009 through 2015. The majority of these events are atmospheric neutrinos and the contribution of atmospheric muons is negligible. Due to an increased selection efficiency and using additional years of data, the statistics increase by more than an order of magnitude compared to previous event selections. The final dataset has been analyzed using two-dimensional likelihood approach in reconstructed muon energy and zenith. The measured astrophysical neutrino flux is compatible with an isotropic, unbroken power-law flux with a normalization of $(0.90^{+0.30}_{-0.27})\times 10^{-18}\,\mathrm{GeV^{-1}\,cm^{-2}\,sr^{-1}\,s^{-1}}$ at $100\,\mathrm{TeV}$ and a spectral index of $2.13 \pm 0.13$. A neutrino flux of only atmospheric origin can be rejected with a significance of $5.6\,{\sigma}$. Compared to previous IceCube measurements with lower energy thresholds the measured spectrum is considerably harder indicating a spectral break in the astrophysical neutrino spectrum of unknown origin. Among the selected events is the highest-energy neutrino observed to date. The event has a reconstructed muon energy of $(4.5\pm1.2)\,\mathrm{PeV}$ and its probability of being of atmospheric origin is below $0.005\%$. Its arrival direction has been reconstructed as $\mathrm{Dec(J2000)}=(11.42\pm0.17)^\circ$ and $\mathrm{RA(J2000)}=(110.63_{-0.55}^{+0.46})^\circ$. Using Monte Carlo simulations the deposited energy within the instrumented volume can be estimated as $(2.6\pm0.3)\,\mathrm{PeV}$ and the median neutrino energy as $8.7\,\mathrm{PeV}$. Even though a muon neutrino is the most likely origin ($88\%$), the probability of a tau ($11\%$) and an electron neutrino ($1\%$) are not negligible. No correlation with high-energy $\gamma$-ray sources has been found. Follow-up analyses with HAWC, HESS, MAGIC and XMM-Newton yield no indication for a source as well. In addition to the highest-energy event 28 events with muon energies above $200\,\mathrm{TeV}$ have been found. No statistical significant correlation with $\gamma$-ray sources could be established