Research Interests:

Nucleons are bound states of quarks and gluons with a spatial extension of the order of 10^-15 m, while nuclei are bound states of nucleons and mesons with an average separation of only a few times the diameter of the nucleons. My main research interest is the interplay of these seemingly disjunct pictures. At what length scale does the "Standard Model" of nuclear physics break down? Hall A at Jefferson Lab is equipped with two identical high-resolution magnetic spectrometers. These, in combination with the intense electron beam at JLAB with an energy of up to 6 GeV, allow us to study in detail the properties of free nucleons and of nucleons embedded in the nuclear medium. So far, accurate results have been obtained for the electric form factor of the proton and of the deuteron up to large values of the momentum transfer. A stringent upper limit has been determined for the strangeness radius of the proton, contributed by pairs of strange quarks. Electron-induced knock-out of protons and of proton pairs is being studied to extract information on the correlation between nucleons in nuclei.