Ph.D. Theses

The emergence of powerful synchrotron sources, fast pixel detectors, and the increasingavailability of high-performance computing has facilitated the acquisition and analysisof high-quality, large-volume diffuse scattering data, providing insights into the realstructures of disordered crystals that were not previously possible. However, its ap-plication to studying local structural order in thin films remains largely unexplored.This limitation arises from the strong substrate contributions, which obscures the weakdiffuse scattering signals from the film, as well as the restricted reciprocal space cov-erage and resolution inherent in grazing incidence X-ray diffraction. [...]

This thesis presents a comprehensive study of the single top quark production in association with a WZ boson pair (tWZ), culminating in the first observation of this process. Measurements of rare processes are crucial to improve our understanding of the Standard Model (SM) and improve the sensitivity to loop-induced new physics. [...]

Die Entdeckung des Higgs-Bosons 2012 am LHC bestätigte das Standardmodell als führende Theorie zur Beschreibung fundamentaler Teilchenwechselwirkungen. Mit größeren Datensätzen konnten die Eigenschaften des Higgs-Bosons immer präziser untersucht werden. [...]

A search for the production of a pair of Higgs bosons ($HH$) via vector-boson fusion (VBF) in the Lorentz-boosted kinematic regime with subsequent decay of the Higgs bosons into four bottom quarks is presented. The analysis is based on 140~fb$^{-1}$ of proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider (LHC), at a center-of-mass energy of $\sqrt{s} = 13$~TeV. [...]

In this thesis, we study different aspects of heavy-quark effects in factorization and resummation using the methods of effective field theories. As the quark masses are much lighter than the hard scale of processes at the LHC, they are considered subleading and usually neglected. [...]

Optische Beobachtungen mit großem Sichtfeld und hoher Kadenz haben jedes Jahr zur Entdeckung mehrerer neuer Quellen am Transientenhimmel geführt. Es wird vermutet, dass bestimmte Arten von Transienten, wie z. [...]

High-power, high-energy, ultrashort, mid-infrared (MID-IR) laser systems operating at high repetition rates are of significant interest for coherent vibrational spectroscopy investigations within the "fingerprint region'' (6-16 um). First of all, the optical properties of Li-based nonlinear crystals (NLC) for MID-IR generation are evaluated under high power laser irradiation at 1030\,nm central wavelength using a thermal imaging method [...]

Free-electron lasers (FELs) require high-quality electron beams with low energy spread, small emittance, and high peak current to enable coherent amplification of light. Laser-plasma accelerators (LPAs) could offer compact and cost-efficient drivers for FELs. [...]

With the discovery of the Higgs boson in 2012 at the Large Hadron Collider at CERN,the final elementary particle predicted by the Standard Model of particle physics wasdiscovered. Since then the study of the Standard Model has focussed on precision mea-surements of various parameters and processes of the theory in the hope of measuringsubtle differences between the theoretically predicted values and those observed in na-ture. [...]

At Free-Electron Lasers (FELs) based on Self-Amplified Spontaneous Emission (SASE), the radiation properties such as pulse duration, arrival time, energy and spectrum fluctuate from shot to shot. To accurately interpret the experimental data on a single-shot basis, dedicated diagnostic tools for each parameter are essential. [...]