Study and characterisation of Low Gain Avalanche Diode (LGAD) for the Time-of-Flight system of the ALICE 3 experiment at LHC

This thesis presents an analysis of the performance of ultra-thin Low-Gain Avalanche Detector (LGAD) prototypes. The analysis consists of an experimental verification of the expected characteristics of these sensors that have become a workhorse for high resolution silicon timing detectors for charged particles and that have been selected as potential candidates for the Time-Of-Flight (TOF) system of the ALICE 3 experiment. As the successor to the current ALICE experiment at CERN, ALICE 3 is envisioned as the prototype for a new generation of heavy-ion collision experiments, and it is expected to start data collection in LHC Run 5 in 2035. The study involved samples of LGAD sensors manufactured by Fondazione Bruno Kessler (FBK) with varying thicknesses, ranging from 50 µm to 15 µm. A key focus of the research was the innovative concept developed in Bologna, known as the double LGAD, designed for timing applications. The characterization of these sensors included standard timing applications with ultra-thin 20 µ- and 15 µ-thick, where the time resolution was measured with charged particles in dedicated beam tests. The results confirmed the excellent temporal performance of these sensors, with resolutions around 20 ps. Additionally, a study on the energy resolution of these sensors was conducted using an ^55Fe source, which emits photons at approximately 6 keV. A comparison of the results obtained with the 20 µm and 15 µm sensors by using charged particles on beam was then carried out to observe how these sensors behaved. The results, including a first comprehensive study of the LGAD energy resolution as a function of gain and sensor thickness, are presented and discussed in details.