Isospin-asymmetry dependence of single-nucleon removal strength
In plain words
When one nucleon is knocked out of a nucleus, experiments find fewer nucleons in each orbit than the simple shell model predicts, a reduction called quenching. In knockout reactions with fast radioactive beams the reduction grows strongly for the more tightly bound kind of nucleon in very neutron- or proton-rich nuclei, while other reaction types show little such trend.
Precise statement
Define $R_s = \sigma_{\mathrm{exp}}/\sigma_{\mathrm{th}}$, the ratio of measured to predicted (shell model times reaction theory) single-nucleon removal cross sections, and $\Delta S$, the separation energy of the removed nucleon minus that of the other species. Intermediate-energy knockout on light targets shows $R_s$ falling from roughly 0.9 to roughly 0.3 as $\Delta S$ goes from about $-20$ to $+20\,\mathrm{MeV}$, whereas transfer, $(p, 2p)$, $(p, pn)$ and $(e, e' p)$ data show weak or no dependence (Aumann et al., Prog. Part. Nucl. Phys. 118, 103847, 2021). Answer: whether the trend reflects nuclear correlations or reaction-model approximations (eikonal and sudden treatment, core excitation), with an ab initio prediction of $R_s(\Delta S)$ consistent across reaction types.
What would settle it
Removal of the same deeply bound nucleon from identical rare-isotope beams by knockout and by quasi-free scattering, analyzed with ab initio overlap functions in a common reaction framework.
Status in the literature
Unverified note
The 2021 community review (Aumann et al.) left the dependence on reaction method unresolved, and it remained debated as of 2026.