Studies of the Microscopic Structure of Hadrons and Hadronic Corrections to Fundamental Properties

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The Pittsburgh group studies spectroscopy of subatomic particles (size less than 1 femtometer) in a variety of ways. They come in two kinds, baryons (e.g. proton) and mesons (e.g. pion). By measuring the masses, widths (effectively lifetime)and decay brancing fractions to the possible final states for each excited state, a large body of information is available as a test for models of the strong interaction. Quantum chromodynamics is strongly felt to be the appropriate theory, but has not been adequately tested in hadron spectroscopy. Experiments must be done at large accelerators; we have been active at Jefferson Lab where a large number of experiments have produced results in the last few years. We were prominent workers in the details of tracking particles in CLAS and had primary responsibility for one of the key results, eta electroproduction. We have also been very active in constructing a theoretical framework and doing complex fits to the data in order to determine the parameters discussed above. Our results are expected to cause major modifications to the Particle Data Group compendium of baryon properties. A new program to study mesons in a particularly clean experimental environment at Cornell Electron Storage Ring has been started.