Performance studies of Low-Gain Avalanche Diodes for the ATLAS High-Granularity Timing Detector

The aim of particle physics to describe the fundamental particles and their interactions. The Standard Model which describes and predicts processes from particle collisions with a high precision, is one of the most successful theories in science. Despite its success, it has several shortcomings and to study those further and look for solutions to them, particle collisions are made in the Large Hadron Collider (LHC) at CERN. ATLAS is one of the experiments that study the collisions at the LHC. To improve the sensitivity for measuring rare processes and finding physics beyond the Standard Model, an upgrade of the LHC is underway. The High-Luminosity LHC (HL-LHC) will dramatically increase the collision rate and the ATLAS detector needs to be upgraded in order to cope with the higher rate. A part of the upgrade of the ATLAS experiment is the High-Granularity Timing Detector (HGTD) which helps to associate produced particles with the correct interactions. To do so, the HGTD uses sensors with high timing precision called Low- Gain Avalanche Diodes (LGADs) which are suited to the high-radiation environment at the HL-LHC. With the higher expected proton-proton collision rate at the HL-LHC, more tracks will mistakenly be associated with the wrong collision. What HGTD does to correctly assign these tracks to the correct collisions, is to apply a separation in time of arrival with a timing resolution of 30 ps per track. If a charged particle hits two or three sensors, this requirement translates to 42 or 52 ps per hit in the sensors. This thesis investigates both the timing resolution and the detector response as a function of position on the surface of the sensors. It can be shown that most of the prototype sensors fulfill the requirement of having less than 42 ps per hit with a uniform response over the surface.