Searching for the e+e- decay of a new particle (X17) created in nuclear transitions of 4He

Abstract

This work concerns an experiment in which an excited state of 4He was produced in an attempt to observer the production of a possible new particle through its de-excitation. The new particle, first described in a 2016 paper and labeled X17, should have mass near 17 MeV/c2, and could be either an J^P = 1^+ or J^P = 0^- particle. To observe such particle, an electron spectrometer was constructed to observe the angular separation of electron + positron pairs depopulating the 20.01 MeV 0- state of 4He. A peak-like enhancement near 115 degrees was observed in this spectrum, which is compatible with the X17 particle. In this thesis, the nuclear processes involved in the experiment are explained, as well as the results from the initial experiment, as well as the titular 4He experiment, with attention also to the data analysis.