Forging the Link between Nuclear Reactions and Nuclear Structure

A review of the recent applications of the dispersive optical model (DOM) is presented. Emphasis is on the nonlocal implementation of the DOM that is capable of describing ground-state properties accurately when data like the nuclear charge density are available. The DOM, conceived by Claude Mahaux, provides a unified description of both elastic nucleon scattering and structure information related to single-particle properties below the Fermi energy. We have recently introduced a nonlocal dispersive optical potential for both the real and imaginary part. Nonlocal absorptive potentials yield equivalent elastic differential cross sections for ${}^{40}$Ca as compared to local ones but change the $\ell$-dependent absorption profile suggesting important consequences for the analysis of nuclear reactions. Below the Fermi energy, nonlocality is essential for an accurate representation of particle number and the nuclear charge density. Spectral properties implied by $(e,e'p)$ and $(p,2p)$ reactions are correctly described, including the energy distribution of about 10\% high-momentum protons obtained at Jefferson Lab. The nonlocal DOM allows a complete description of experimental data both above (up to 200 MeV) and below the Fermi energy in $^{40}$Ca. It is further demonstrated that elastic nucleon-nucleus scattering data constrain the spectral strength in the continuum of orbits that are nominally bound in the independent-particle model. Extension of this analysis to $^{48}$Ca allows a prediction of the neutron skin of this nucleus that is larger than most predictions made so far.Comment: 15 pages, 8 figures; Conference proceedings of CNR*15 workshop, Tokyo, October 2015 to be published in EPJ Web of Conference

Asymmetry dependence of proton correlations

A dispersive optical model analysis of p+40Ca and p+48Ca interactions has been carried out. The real and imaginary potentials have been constrained from fits to elastic scattering data, reaction cross sections, and level properties of valence hole states deduced from (e,e'p) data. The surface imaginary potential was found to be larger overall and the gap in this potential on either side of the Fermi energy was found to be smaller for the neutron-rich p+48Ca system. These results imply that protons with energies near the Fermi surface experience larger correlations with increasing asymmetry.Comment: 4 pages, 5 figure

Self-consistent Green's function calculation of 16O at small missing energies

Calculations of the one-hole spectral function of 16O for small missing energies are reviewed. The self-consistent Green's function approach is employed together with the Faddeev equations technique in order to study the coupling of both particle-particle and particle-hole phonons to the single-particle motion. The results indicate that the characteristics of hole fragmentation are related to the low-lying states of 16O and an improvement of the description of this spectrum, beyond the random phase approximation, is required to understand the experimental strength distribution. A first calculation in this direction that accounts for two-phonon states is discussed.Comment: Proceedings of ``Nuclear Forces and the Quantum Many-Body Problem'', INT, Oct. 4-8, 200

Pairing properties of nucleonic matter employing dressed nucleons

A survey of pairing properties of nucleonic matter is presented that includes the off-shell propagation associated with short-range and tensor correlations. For this purpose, the gap equation has been solved in its most general form employing the complete energy and momentum dependence of the normal self-energy contributions. The latter correlations include the self-consistent calculation of the nucleon self-energy that is generated by the summation of ladder diagrams. This treatment preserves the conservation of particle number unlike approaches in which the self-energy is based on the Brueckner-Hartree-Fock approximation. A huge reduction in the strength as well as temperature and density range of ${}^3S_1$-${}^3D_1$ pairing is obtained for nuclear matter as compared to the standard BCS treatment. Similar dramatic results pertain to ${}^1S_0$ pairing of neutrons in neutron matter.Comment: 15 pages, 10 figure

Density and isospin asymmetry dependence of high-momentum components

We study the one-body momentum distribution at different densities in nuclear matter, with special emphasis on its components at high momentum. Explicit calculations for finite neutron-proton asymmetry, based on the ladder self-consistent Green's function approach, allow us to access the isospin dependence of momentum distributions and elucidate their role in neutron-rich systems. Comparisons with the deuteron momentum distribution indicate that a substantial proportion of high-momentum components are dominated by tensor correlations. We identify the density dependence of these tensor correlations in the momentum distributions. Further, we find that high-momentum components are determined by the density of each sub-species and we provide a new isospin asymmetry scaling of these components. We use different realistic nucleon-nucleon interactions to quantify the model dependence of our results.Comment: 14 pages, 7 figures, 1 table. Accepted version in Phys. Rev.

Pairing and short-range correlations in nuclear systems

The structure and density dependence of the pairing gap in infinite matter is relevant for astrophysical phenomena and provides a starting point for the discussion of pairing properties in nuclear structure. Short-range correlations can significantly deplete the available single-particle strength around the Fermi surface and thus provide a reduction mechanism of the pairing gap. Here, we study this effect in the singlet and triplet channels of both neutron matter and symmetric nuclear matter. Our calculations use phase-shift equivalent interactions and chiral two-body and three-body interactions as a starting point. We find an unambiguous reduction of the gap in all channels with very small dependence on the NN force in the singlet neutron matter and the triplet nuclear matter channel. In the latter channel, short range correlations alone provide a 50% reduction of the pairing gap.Comment: Final version, as published in journal after refereein