SPECTROSCOPIC FACTORS FOR NUCLEON KNOCK-OUT FROM O-16 AT SMALL MISSING ENERGY

Spectroscopic factors for one-nucleon knock-out from O-16 are calculat ed for states with low excitation energy in N-15 with the Bonn-C poten tial. A method is proposed to deal with both short- and long-range cor relations consistently. For this purpose a Green's function formalism is used and the self-energy in the Dyson equation is approximated as t he sum of an energy-dependent Hartree-Fock (HF) term and dispersion an d correlation terms of higher order in the G-matrix interaction. This G matrix is obtained by solving the Bethe-Goldstone equation with a Pa uli operator which excludes just the model space treated in the subseq uent calculation of the self-energy. The energy dependence of the HF e nergies induces an additional reduction of the spectroscopic factors f or quasiparticle states close to the Fermi level by about 10%. Experim ental data may signal the need of some further improvement in the trea tment of intermediate- and long-range correlations.