A study of the structure of nucleons and the role of quarks in determining this structure will be performed using the tagged photon system in Hall B at the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory). The photon tagger, which was in large part designed and built by the Catholic University of America (CUA) group, measures the energy of the photon that produces a reaction in a nuclear target. The reaction products are then measured by the CEBAF Large Acceptance Spectrometer (CLAS). The CUA group is an active participant in the CLAS Collaboration, a partnership of many user groups devoted to constructing, and using the instrumentation in Hall, B to perform a variety of experiments concurrently. During the initial phase of the CLAS program, the CUA group is most deeply involved in two experiments: the photoproduction of strange particles (K mesons and hyperons), and the helicity structure of pi meson photoproduction. The former experiment, designed to probe the role of strange quarks in the proton, will provide a data sample more than 100 times larger than that previously available. The latter, requiring both a polarized photon beam and a polarized proton target, will constitute part of a test of the Drell- Hearn-Gerasimov sum rule, a fundamental quantity of worldwide interest. The CUA group is also participating in two experiments which use the tagged photon beam without the CLAS: a measurement of the photofission probabilities for heavy nuclei, and a measurement of the rare decays of the phi meson.
