Electromagnetic Form Factors of Hadrons in the Space-Like Region

Abstract

The theory of the strong force is unique amongst the known forces of nature in that the strength of its interactions grow with distance. It is postulated that this leads to the empirically observed colour con nement hypothesis. This hypothesis states that quarks and gluons, the fundamental degrees of freedom in the strong force form together into complex bound states called hadrons, rather than appearing as free particles. Thus the study of the strong force becomes the study of hadrons and their structure. One way we may study the structure of these composite bound states is through their electromagnetic interactions. In particular, information may be drawn about the structure of these hadrons from their elastic scattering data in the form of the hadron's electromagnetic form factors. In this thesis, predictions are made of the nucleon and hyperon electromagnetic form factors by utilizing a non-perturbative quark model dressed by a pion cloud. Constraints from chiral symmetry arguments lead us to propose performing these chiral loop e ects at the hadron level which leads to an improvement in a number of low energy observables related to the electromagnetic form factors. The extraction of the pion form factor from pion electroproduction is also studied in detail. Constraints from gauge invariance are used to argue that the current model used to extract the pion form factor may be too simplistic. We study the model dependence in the context of a simple toy model, and nd that the possible errors associated with this approximation could be as large as ten percent. We then proceed to perform a more in-depth calculation with a more sophisticated model, and show that the qualitative e ects are the same. Together, these two studies imply that current measurements of the pion form factor are overestimated.