Ph.D. Theses

This thesis presents a search for a pair of light pseudoscalar bosons produced from the decays of the 125 GeV Higgs boson, focusing on final states with four tau leptons. This searchis motivated by numerous beyond the standard model theories that predict an extended scalar sector, introducing a wide array of new physical states beyond the single Higgs boson observed in the standard model. [...]

Digital Silicon Photomultipliers (dSiPMs) and Monolithic Active Pixel Sensors (MAPS) are emerging technologies, fabricated using commercial Complementary Metal-Oxide-Semiconductor (CMOS) processes. These detectors have the potential to become key components in High-Energy Physics (HEP), with the ability to meet the demanding requirements of future experiments. [...]

This thesis investigates the fundamental processes governing supercapacitors with aqueous electrolytes through the development and application of in-situ and operando synchrotronand neutron techniques. Using a suite of complementary methods, including X-ray Transmission (XRT), X-ray Fluorescence (XRF), (Anomalous) Small-Angle X-ray Scattering ((A)SAXS), Small-Angle Neutron Scattering (SANS), X-ray Diffraction (XRD), and Neutron Diffraction (ND), a detailed experimental framework is established to probe supercapacitor behaviour under working conditions. [...]

The LEAP (Laser Electron Acceleration with Polarization) project at DESY is a proof-of-principle experiment aiming to demonstrate the generation -- thus also the transport -- of spin-polarized electron beams from a laser-plasma accelerator (LPA). This is expected to be achieved using a pre-polarized plasma source, generated via the photodissociation of HCl molecules with an ultraviolet (UV) dissociation laser. [...]

Simulating particle interactions within high-energy physics detectors is essential for interpretingexperimental data and advancing our understanding of fundamental physics. Calorimetersmeasure particle energies through cascades known as showers, but their complex responsesand the computational intensity of traditional simulation tools like Geant4 posesignificant challenges. [...]

Quantum materials are governed by a complex interplay of spin, orbit, charge and lattice degrees of freedom, resulting in emergent phenomena like high-temperature superconductivity, charge and orbital ordering and insulator-to-metal transitions (IMTs). Often, the interaction of these subsystems results in an energy landscape with multiple local minima favouring different phases. [...]

In this thesis, we report recent advancements in the understanding of Higgs branch moduli spacesof six-dimensional (1,0) supersymmetric quantum field theories, along with related developments.These progresses have been achieved by exploiting the interplay between geometrical engineeringand techniques in quiver gauge theories, leading to new insights into the Higgs mechanism’s actionin higher-dimensional supersymmetric theories.Paper I: We present an extension of the magnetic quiver technique to a class of non-gravitationalsupersymmetric quantum field theories in six dimensions known as Little String Theories (LSTs).These theories also exhibit a higher-group symmetry structure. Notably, we prove a monotonicitytheorem describing the evolution of κR, a quantity characterizing the higher group symmetry, underpartial Higgsing patterns.Paper II: Specializing to a brane engineering framework, we construct a family of LST modelswith a natural interpretation as an F-theory compactification. [...]

Two analyses related to the inclusive determination of the magnitude of the Cabbibo-Kobayashi-Maskawa matrix element $|V_{ub}|$ are presented. The first analysis presents the first measurement of the ratio of partial branching fractions of the inclusive charmless, $\overline{B} \to X_u \ell \overline{\nu}$, to the inclusive charmed, $\overline{B} \to X_c \ell \overline{\nu}$, semileptonic $B$ decay, where $\ell$ represents an electron or muon, and $X$ a hadronic system. [...]

Synchrotron radiation sources and free-electron lasers have revolutionised the study of matter and biological systems by providing unique combinations of radiation pulse characteristics. Although these two types of facilities differ fundamentally in terms of pulses time scales, coherence properties, and (peak) brilliance, each offers an exceptional mix of these features. [...]

Die Untersuchung der Wechselwirkung von Röntgenstrahlen mit biorelevanter Materie ist ein anhaltendes und weitverbreitetes Forschungsfeld. Obwohl die makroskopischen Folgen dieser Wechselwirkung bereits weitgehend verstanden sind, ist unser Verständnis der Prozesse auf molekularer Ebene noch sehr unzureichend. [...]