LONG-RANGE CORRELATIONS AND THE MOMENTUM DISTRIBUTION IN NUCLEI

The influence of correlations on the momentum distribution of nucleons in nuclei is evaluated starting from a realistic nucleon-nucleon inte raction. The calculations are performed directly for the finite nucleu s O-16 making use of the Green function approach. The emphasis is focu sed on the correlations induced by the excitation modes at low energie s described within a model space of shell-model configurations includi ng states up to the sdg shell. Our analysis demonstrates that these lo ng-range correlations do not produce any significant enhancement of th e momentum distribution at high missing momenta and low missing energi es. This is in agreement with high-resolution (e, e'p) experiments for this nucleus. We also try to simulate the corresponding effects in la rge nuclei by quenching the energy spacing between single-particle orb its. This yields a sizable enhancement of the spectral function at lar ge momenta and small energy. Such behavior could explain the deviation of the momentum distribution from the mean-field prediction, which ha s been observed in (e, e'p) experiments on heavy nuclei like Pb-208.