Role of Long-Range correlations in the quenching of spectroscopic factors

We consider the proton and neutron quasiparticle orbits around the closed-shell Ni56 and Ca48 isotopes. It is found that large model spaces (beyond the capability of shell model applications) are necessary for predicting the quenching of spectroscopic factors. The particle-vibration coupling is identified as the principal mechanism. Additional correlations-due to configuration with several particle-hole excitations-are estimated using shell model calculations and generate an extra reduction which is □4% for most quasiparticle states. The theoretical calculations nicely agree with (e, e′p) and inverse kinematics knockout experiments. These results open a new path for a microscopic understanding of the shell model.