Ph.D. Theses

Future e+e− colliders, such as the FCC-ee, aim to test the Standard Model to the ultimateprecision. This requires synergistic progress in detector technology and data analysis techniques.This thesis comprehensively presents the interlinked efforts targeting these goals.Jet flavour identification algorithms play a crucial role in maximally exploiting the physicspotential of the FCC-ee, particularly in the Higgs and electroweak sectors. [...]

The FCC-ee is the first stage of a two stage project which would envision a 92 km tunnelbeing used for an electron-positron collider experiment starting around 2045, and a proton-proton collider in the 2070’s. The FCC-ee offers unprecedented precision tests of the StandardModel, owing to its clean leptonic collision environment and exquisite luminosity [...]

This thesis presents precise determinations of two fundamental parameters of the stan-dard model (SM), the strong coupling constant αS (mZ) and the top quark mass mtalong with its width Γt. These contribute importantly to constraints on the stabilityof the SM electroweak vacuum.For the determination of αS (mZ), CMS inclusive jet measurements using LHC proton-proton (pp) collisions at centre-of-mass energies √s = 2.76, 7, 8, and 13 TeV are anal-ysed together, for the first time. [...]

Gauge-mediated supersymmetry breaking models provide a compelling framework for the search for a supersymmetric partner of the tau lepton ($\widetilde{\tau}$) with a macroscopic lifetime. In such scenarios, $\widetilde{\tau}$ can decay to tau lepton displaced from the primary proton-proton interaction vertex. [...]

This thesis presents a search for direct Charge-Parity (CP) violation in the decay τ− →π−K0Sντ (≥ 0π0) using data collected by the Belle II experiment, corresponding to an integratedluminosity of 365 fb−1. The analysis is motivated by a previous BABAR measurement, which reported a 2.8σ deviation from the Standard Model prediction. [...]

The Standard Model's known limitations drive the search for new physics, a major focus of modern experimental particle physics. This thesis presents two searches for Beyond the Standard Model physics in the four-top-quark final state at the ATLAS experiment. [...]

Conformal Field Theories (CFTs) are special classes of quantum field theories thatfind applications ranging from critical phenomena to theories of quantum gravity viaholography. Understanding thermal effects in CFTs is crucial: criticality is experimen-tally probed at finite temperature, and, from the holographic perspective, the studyof thermal CFTs is dual to the study of black holes in Anti-de Sitter space. [...]

Hard X-rays generally only interact very weakly with matter, so that tissue, for example, is quite transparent to them. However, this makes the controlled manipulation of X-ray light particularly challenging. [...]

In the Standard Model of Particle Physics, all leptons have the same coupling strength tothe weak interaction. Comparing the theoretical model with experimental observations revealsa slight deviation in the electron branching fraction of τ -lepton decays. [...]

Kosmische Strahlung und hochenergetische Neutrinos stammen aus extremen astrophysikalischen Umgebungen, wo kosmische Strahlen mit Materie oder Photonen interagieren und Neutrinos erzeugen. Die auf der Erde beobachtete Flavour-Zusammensetzung liefert Einblicke in deren Ursprünge. [...]