Radiative transitions in quarkonium

Quantum Chromo Dynamics (QCD) is the theory of strong interactions and in principle all static and dynamic properties of hadrons could be calculated. In practice, however, most computations prove to be too difficult to perform due to the complexity of the theory. That's why we have to look for other methods to describe the hadrons. One approach is to discretize space-time and to do QCD calculations with the aid of fast powerful computers: lattice QCD. Another is to leave QCD for what it is and follow a more empirical approach: what can we learn about the interquark interaction from the data? The latter method is a phenomenological one and is the one followed in this thesis. The other one which here is presented is the Unitarized Meson model of the Nijmegen group. This model tries to describe properties of quarkonium in consistent way. Our model is essentially non-relativistic and therefore heavy quarkonium that is, charmonium and bottomium, is particularly suited to be described by this model and that is where the emphasis lies in this thesis. Our aim is to extract information from experimentally obtained data by comparing these data with results from this model. A satisfactory agreement gives an indication of the correctness of the assumption underlying the model. And this, in turn, will hint at the correct form of the interaction between (anti)quarks, which will bring us one step further in the process of unraveling the secrets of nature. (author). 71 refs., 14 figs., 24 tabs