An experimental setup for the detection of e+e- pairs in the decay of 8Be*

The existence of a light neutral boson, possible mediator of a new fundamental interaction, has been recently proposed by A.J. Krasznahorkay and collaborators. A series of experiments was carried out at the Atomki laboratory (Debrecen,Hungary) measuring electron-positron pairs emitted in the decay of excited 8Be and 4He. Anomalies in the e+e− angular correlation distributions with respect to the Internal Pair Creation (IPC) process have been reported. The first results concern the decay of the 18.15 MeV 1+ state in 8Be, while the group later focused on the ≈20 MeV excited states in 4He. In order to explain the reported anomaly several interpretation have been developed. The approach proposed by X. Zhang and G. Miller aims to describe the anomalies in an almost conventional nuclear physics framework, improving the reaction modeling. Conversely, a possible interpretation given by J. Feng and collaborators involves the appearance of a new gauge vector boson, called X17, that could possibly mediate the interaction between the SM and the dark sector. The Atomki results and the related interpretations triggered a renewed interest in the spectroscopy of light ions by Internal Pair Creation. At this purpose, a new experimental setup is being developed at the INFN Legnaro National Laboratories of INFN (Legnaro, Padova, Italy). The first goal is to provide an independent replica of the Hungarian experiment. This thesis work focuses on a complete simulation of the proposed setup and reports about the first experimental characterization of the prototype detectors. The text is organized as follows: after a short introduction on the physics of electromagnetic transitions and internal pair production in nuclei, the state of the art regarding the 8Be and the 4He anomalies will be discussed, explaining the roots of the X-boson or X17 case. Afterwards, the simulation and the experimental characterization works will be reported.