PROTON SPECTRAL FUNCTIONS AND MOMENTUM DISTRIBUTIONS IN NUCLEI FROM HIGH-RESOLUTION (E,E'P) EXPERIMENTS

Recent high-precision data obtained with approximately 100 keV resolution in the missing mass variable of the proton knockout-reaction induced by electrons of 500 MeV are reviewed. The high-resolution feature has allowed the observation of knockout from quantum states at the Fermi-surface that are closely spaced in energy. Data are discussed for several nuclei ranging from the deuteron to 208Pb. In the few-body systems (A=2,3,4) and in 6Li the data are fairly well reproduced by 'exact' calculations. For heavier nuclei the ingredients and approximations of a distorted wave impulse approximation treatment of the (e,e′p) reaction are discussed in detail. For mass A>or=12 systems a systematic reduction of spectroscopic strength is observed amounting to 40-50% of the full-shell value expected in the mean field approximation to the nuclear many-body wavefunction. The author gauges the limits of validity of the mean field approximation and compare the (e,e′p) data to microscopic calculations of the effect of NN correlations on the proton spectral function and momentum distribution. Evidence is adduced for a substantial depletion of quantum states near the Fermi-surface. For deeper-hole states the depletion is found to be smaller, in keeping with theoretical expectations. Finally, a review is presented of future experiments in an enlarged kinematics domain that will address the physics of nucleon-nucleon correlations in many-body fermion systems with new experimental and theoretical tools.