Spectroscopy and correlations probed in direct two-nucleon knockout reactions

Nucleon knockout reactions from fast radioactive secondary beams colliding with light nuclear targets provide a useful tool for studying structure away from the valley of (β-stability. An efficient means of producing specific exotic nuclei, the technique has been recently applied to study nuclear halos, isospin symmetry and cross-shell excitations, and in tracking the evolution of single-particle states, and probing the associated quenching (N=20, N=28) and emergence (N=16) of shell gaps. Recent theoretical work has demonstrated the sensitivity of residue momentum distributions following two-nucleon removal to the underlying structure. In particular, there is a sensitivity to the total orbital angular momentum of the removed pair, providing additional tests of (shell- or many-body-) structure-model two-nucleon overlaps. We illustrate the structural sensitivities in the context of nucleon knockout from ¹²C and ¹⁶O, and discuss the prospects for studying np-correlations along the N = Z line, highlighting the need for new final-state exclusive measurements, including those with stable beams.