Partial-wave analysis of the radiative decay of J/psi into p pbar

The Standard Model describes the smallest building blocks of our universe, so-called quarks and leptons, and the forces that act on them. The building blocks can bundle into larger and heavier particles. These composite particles are called hadrons. One of the best-known hadrons is the proton. The Higgs boson, which was first detected in 2012, explains how the smallest building blocks get their mass. However, the Higgs mechanism only explains 1% of the mass of the proton. The other 99% arises from internal strong forces that are not yet well-understood. To better understand the 99%, it is important to study the production of hadrons in different processes, and to obtain information from as many different decay reactions as possible. Hadrons of the charmonia group, such as J/psi and the ground state eta_c, are highly suitable particles for this, and result in a relatively easy-to-interpret spectrum of narrow peaks that do not overlap. In this thesis the radiative decay of J/psi into a proton (p) and antiproton (pbar) is studied. The aim of this study was to gain a better understanding of the full spectrum of the proton-antiproton invariant mass, and especially to gain more insight into the poorly-understood properties of the intermediate resonance eta_c. In this study, a special multidimensional analysis, a so-called partial-wave analysis, was applied for the first time to the radiative decay from J/psi to eta_c. This study is based on data taken by the Beijing Spectrometer (BES) III, which has collected world's largest dataset of J/psi reactions.