Not yet reviewed by Pith; the record is open.

The systematic quenching of spectroscopic factors in terms of separation energy asymmetry in single-nucleon knockout reactions remains a puzzle. We propose a core screening effect to consider the hindrance when strongly bound nucleons in the projectile nucleus are removed by the heavy-ion target. The core screening effect is simulated as a density dependent suppression of single-particle wave functions inside the core of projectile. Our study shows that the parameterized core screening effect can significantly reduce the isospin dependence of quenching factors, offering insights into nuclear reaction mechanisms.