Longitudinal momentum distributions of the reaction residues following fast two-nucleon knockout reactions

The longitudinal momentum distributions of the cross sections of heavy projectile-like residues after fast, direct two-like-nucleon knockout reactions are discussed. Both the two-nucleon inelastic breakup (stripping) and the stripping-diffraction removal events are considered. We show that, because the two mechanisms have a very similar nuclear surface localization, they generate essentially identical longitudinal momentum distributions. The approach used combines reaction dynamics, using the sudden, eikonal and spectator-core approximations, with structure wave functions from the many-body shell model. The sensitivities of the resulting longitudinal momentum distributions to the orbital angular momenta, the separation energies, and the angular momentum coupling of the two removed nucleons are clarified. In particular, the widths of these distributions are shown to provide a very clear signal of the total angular momentum of the removed-nucleon pair--pairs coupled to larger total angular momentum giving broader distributions. These now complete distributions, from correlated wave functions, are significantly different from earlier uncorrelated estimates. Confirmation of these theoretical expectations is presented, based on very recent intermediate-energy, residue final-state inclusive and exclusive two-nucleon removal measurements.