Study of a detection system for the search of the X17 boson at the n_TOF facility

In recent years, a statistically significant anomaly has been observed in the emission of electron-positron pairs with an invariant mass of approximately 17 MeV c-2 at the HUN-REN ATOMKI laboratories. This so-called X17 anomaly consisted of an excess of events in the angular distribution of lepton pairs produced in the nuclear reactions 7Li(p,e+e-)8Be, 3H(p,e+e-)4He and 11B(p,e+e-)12C. Among several hypotheses, this anomaly may indicate the existence of a light neutral boson beyond the Standard Model. However, further independent experimental validation is needed to either confirm or refute these observations. For this purpose, the conjugate neutron-induced reaction 3He(n,e+e-)4He has been proposed to be studied at the n_TOF facility. The measurement of angular distribution of the electron-positron pair produced in this reaction could confirm the existence of the X17 boson and, if detected, determine its quantum numbers. The detection system for this experiment is designed to provide large acceptance, particle identification and tracking. It consists of a layer of micro-RWELL gaseous detectors and a surrounding array of scintillator bars. This thesis presents the characterization of the scintillator array, performed through data analysis of a test conducted at n_TOF. The role of the array in the experiment is to trigger the acquisition and to measure the incident neutron energy. Noise and saturation effects, which are crucial aspects in a neutron-dominated background, were evaluated for both the scintillator and the readout system. A hit-map reconstruction algorithm was implemented to improve the overall tracking resolution. While the scintillator array and SiPM readout were found suitable for the upcoming experiment, the data acquisition (DAQ) system showed several limitations, prompting the selection of an alternative system for the final setup.