Dynamical Origin of Spectroscopic Quenching in Knockout Reactions

Abstract

Nucleon-removal reactions are a primary tool for extracting single-particle structure of rare isotopes, yet the ratio $R_s={\sigma }_{\exp }/{\sigma }_{\mathrm{th}}$ of measured to theoretical cross sections drops systematically below unity for deeply bound nucleons. I derive the exact effective three-body Hamiltonian for composite-projectile reactions using a sequential double Feshbach projection and show that the standard additive model misses two induced interactions: a non-additive term from virtual target excitations and a polarization potential from excluded projectile configurations. Their omission overestimates the stripping cross section, producing apparent quenching distinct from genuine nuclear-structure correlations. This mechanism offers a dynamical origin for the strong separation-energy dependence of the quenching ratio, a feature unique to knockout analyses. Existing four-body CDCC calculations for ${}^6$Li validate the framework: the proper Feshbach reference reproduces elastic scattering data, while a phenomenological optical potential double counts the breakup absorption and fails.