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Spectroscopy
and Structure of the Nucleon The nature of QCD confinement provides an ongoing challenge to our understanding of soft QCD. Studying the baryon spectrum provides one avenue to learn more about this unique feature since the location and properties of excited states reflect the dynamics and relevant degrees of freedom within hadrons. Through decades of analyses of data from both hadronic and electromagnetic scattering experiments, numerous baryon resonances have been found, and their masses, widths, and quantum numbers have in many cases been determined. However, many additional states have been predicted by quark models. If they exist, these states have either eluded detection or have produced only faint signals in the existing data sets. The search for such resonances provides a natural motivation for many of the current and future measurements at JLab described in this section. A more complete knowledge of the resonance spectrum would be invaluable to studies that aim to elucidate the detailed dynamics and degrees-of-freedom responsible for the baryon spectrum. These include QCD lattice calculations, various constituent quark models, QCD sum rules, and unitary Chiral Perturbation Theory. For example, there is the interesting possibility of chiral-symmetry restoration exhibited by the high-lying (and poorly determined) states [Nef98]. It is equally important to have precisely determined properties for the well-established resonances, as these are likely to be less model-dependent, and existing data suggest deviations from constituent-quark-model predictions for their decay properties [Cap00]. Because we plan to extend our cross-section measurements to include strangeness and spin observables, our experimental program in baryon spectroscopy should contribute significantly towards achieving these goals. Our photopion studies are summarized in Sections 1-5 below, our work on photoproduction of strange particles in Sections 6-8, and our work on the structure functions of the nucleon in Section 9.
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