Thesis defense of Pascal Thomas Gutjahr

The atmospheric muon flux provides a powerful probe of TeV-to-PeV hadronic interactions in air showers and offers unique access to particle production in the forward kinematic region that is not accessible at collider experiments. While the conventional flux from pion and kaon decays is comparatively well understood, the prompt component, dominated by decays of charmed hadrons, lacks precise experimental constraints at the highest energies. The atmospheric muon flux is also a dominant background for astroparticle analyses, in particular searches for astrophysical neutrino sources. This thesis presents a measurement of the atmospheric muon flux, including its prompt component, using 12.12 years of data from the IceCube Neutrino Observatory. The muon energy spectrum is unfolded to surface level in the range 10 TeV to 15 PeV, extending previous IceCube measurements by roughly an order of magnitude in energy. A key contribution of this work is a machine learning-based reconstruction of the energy of the leading muon (the most energetic muon within a bundle), increasing sensitivity to the spectral differences between conventional and prompt components. New CORSIKA simulations were produced to tag muons of prompt or conventional origin, and a dedicated event selection was developed for this analysis. The unfolded flux is compared with MCEq and CORSIKA predictions for several combinations of primary cosmic-ray and hadronic interaction models. Among the models considered here, the MCEq prediction using the GlobalSplineFit primary cosmic-ray model together with SIBYLL 2.3c provides the best agreement with the high-energy unfolded flux. For this prediction, the prompt atmospheric muon flux is observed with a significance of 4.4 sigma. Several models have been tested and prompt and conventional normalizations are determined, with most fits exceeding 5 sigma. The results provide new experimental constraints on forward charm production in air showers and will contribute to ongoing investigations of the muon deficit in air shower experiments.