Physics for Particle Detectors and Particle Detectors for Physics - Timing Performance of Semiconductor Detectors with Internal Gain and Constraints on High-Scale Interactions of the Higgs Boson

Experimental particle physics is a science of many scales. A large number of physical processes spanning energies from meV to TeV must be understood for modern collider experiments to be designed, built, and conducted successfully. This thesis contributes to the understanding of phenomena across this entire dynamic range. The first half of this document studies aspects of low-energy physics that govern the operation of particle detectors, limit their performance, and guide the development of novel instrumentation. To formalise these aspects, classical electrodynamics is used to derive a general description of the formation of electrical signals in detectors, and ideas from quantum mechanics are applied to the study of charge avalanche amplification in semiconductors. These results lead to a comprehensive analytical characterisation of the time resolution and the efficiency of single-photon avalanche diodes, and isolate the most important design variables. They also reveal the applicability of these devices in precision timing detectors for charged particles, which is experimentally verified in a high-energy hadron beam. Large detector systems at hadron colliders probe fundamental physics at the energy frontier. In the second half, data collected with the ATLAS detector during Run 2 of the Large Hadron Collider are used to measure the cross-section for the production of a Higgs boson together with an electroweak boson as a function of the kinematic scale of the process. This measurement provides the finest granularity available to date for this process. It is highly informative of the structure of interactions beyond the direct kinematic reach of the experiment, and new limits are set on the couplings of such interactions within an effective field theory.

Philipp Windischhofer is a particle physicist and member of the ATLAS Collaboration at the European Organization for Nuclear Research (CERN) in Geneva, Switzerland. A main focus of his work concerns the experimental investigation of the Higgs boson, the only spin-zero particle thus far observed in nature. He contributes to this program through the analysis of collider data and the development of new data analysis techniques. He is also heavily involved in the study and development of particle detectors. Together with his collaborators, he derives first-principles descriptions of the mechanisms underlying these instruments, thereby pinning down their ultimate performance limits and leading the way towards novel applications of existing technologies. Currently, Philipp is developing a fast numerical code for the simulation of radio-wave emissions from ultra-high energy particles reaching Earth from outer space. He completed his doctoral research at the University of Oxford in 2022, and is now working as a postdoctoral researcher at the University of Chicago (USA).