Light Baryon Spectroscopy - Recent Results from Photoproduction Experiments

One of the open challenges in subnuclear physics is to understand the non-perturbative regime of QuantumChromodynamics, including the world of the nucleon and its excitations.
While the underlying gauge theory, Quantum Chromodynamics (QCD), is well established, the non-perturbative phenomenon of structure formation - the fundamental fields (the quarks and gluons) only appear within bound states (mesons and baryons) and their excitations - is not yet understood.

One of the key issues is to identify the relevant degrees-of-freedom and the effective forces between them.
A necessary step towards this aim is undoubtedly a precise knowledge of the experimental spectrum and the properties of baryon resonances.
Recently, photoproduction experiments have made large progress providing not only differential cross section measurements but also high quality single and double polarisation observables, leading to a better understanding of the experimental spectrum of baryon resonances.

In the talk, among other results, results from the recent double polarisation experiments at ELSA will be discussed.