between, mesons and nucleons. These particles, their properties, and their
interactions form the fundamental components of any description of the structure
of nuclei. Recently, our group has focused most of its emphasis on pseudoscalar
strangeness-zero meson photoproduction from nucleons. This group participates
as full members in collaboration activities with the CEBAF Large Acceptance
Spectrometer (CLAS) Collaboration.
Quantum chromodynamics (QCD) provides a successful description of the phenomena associated with elementary particles at high energies. Yet, extending that understanding to the low-energy, non-perturbative regime is hampered by severe limitations in our knowledge of the excitations of the nucleon and light mesons. Since the excitation spectra for nucleons and mesons still possess major gaps and ambiguities, any QCD-based description of those hadrons -and, therefore, any attempt to embed that understanding in nuclear matter- faces severe handicaps. With such deficiencies in our knowledge of nucleon and meson properties, the transition between the non-perturbative and perturbative energy regimes remains mysterious.
This research and education program utilizes polarized tagged photon beams in Hall B at Jefferson Lab to reveal new details of light hadron structure and to help isolate
the quark and gluon angular momentum and spin contributions within hadrons. The
work provides data on polarization observables in meson photoproduction, including
double polarization observables, many of which have never been measured before.
These data are absolutely necessary for progress in understanding the structure of the
nucleon. This program also investigates the extension of these studies above the few
GeV photon energy region through participation in Hall D at Jefferson Lab, opening
up the possibility of producing and identifying exotic meson states, which permit
probing excitations of the gluonic flux tubes between quarks.