The excited baryon spectrum: What have we learned?

One of the most striking phenomenon of quantum chromodynamics (QCD) is the formation of the nucleon out of massless gluons and almost massless quarks. This system of confined quarks and gluons serves as the basic constituent of ordinary baryonic matter and exhibits the characteristic spectra of excited states, which are sensitive to the details of quark confinement. Complementary to nucleon structure studies in deep inelastic scattering experiments, nucleon excitations provide the unique opportunity to explore the many aspects of non-perturbative QCD. The last few years have seen significant progress toward the mapping of the nucleon spectrum. The rapidly growing database of high-quality experimental results on exclusive meson photoand electroproduction on the nucleon from experimental facilities around the world now allows the hadron spectroscopy community to determine the scattering amplitudes of the underlying reactions more accurately and to identify nucleon resonance contributions with minimal model dependence. At Jefferson Laboratory (JLab), the excited baryon program now continues in the 12-GeV era with the successful data-taking of the GlueX experiment. Part of the GlueX scientific program is to search for and study the poorly-known multi-strange baryons which will provide an important missing link between the lightand the heavy-flavor baryons.