Investigating new Pulse Shape Discrimination parameters to improve background suppression in LEGEND-200

The search for neutrinoless double beta decay (0νββ) is one of the main goals in modern particle physics, as its discovery would prove that neutrinos are Majorana particles and that lepton number is not conserved. The LEGEND-200 experiment uses enriched high purity germanium (HPGe) detectors to reach the very low background level required to explore half-lives above 1027 years. This thesis studies the performance of the pulse-shape discrimination (PSD) methods used in LEGEND-200 to identify and remove background events. The analysis focuses on the maximum amplitude of the current pulse over amplitude of the charge pulse (A/E) and Late Charge (LQ) parameters, evaluated for PPC, ICPC, and BEGe detector types using 228Th calibration data. Physics data from two running conditions are compared: Periods 03–09, when the nylon mini-shroud (NMS) was installed, and Period 11, after its removal. Although the removal of the NMS changed the composition of the background, the PSD methods continued to suppress high-energy surface events effectively. A new timing parameter, LQ_Amax, was also tested and found to be useful for de scribing the late-charge region, especially for PPC detectors. Overall, the results confirm that the LEGEND-200 PSD approach remains stable and efficient in reducing the various types of background events that plague the experiment.