Faddeev treatment of long-range correlations and the one-hole spectral function of O16

The Faddeev technique is employed to study the influence of both particle-particle and particle-hole phonons on the one-hole spectral function of O16. Collective excitations are accounted for at a random phase approximation level and subsequently summed to all orders by the Faddeev equations to obtain the nucleon self-energy. An iterative procedure is applied to investigate the effects of the self-consistent inclusion of the fragmentation in the determination of the phonons and the corresponding self-energy. The present results indicate that the characteristics of hole fragmentation are related to the low-lying states of O16.Comment: 10 pages, 6 figures, 3 tables. Submitted to Phys.Rev.

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

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

Toward a Global Dispersive Optical Model for the Driplines

A dispersive-optical-model analysis has been performed for both protons and neutrons on 40,42,44,48Ca isotopes. The fitted potentials describe accurately both scattering and bound quantities and extrapolate well to other stable nuclei. Further experimental information will be gathered to constrain extrapolations toward the driplines.Comment: Invited talk at the "10th International Conference on Nucleus-Nucleus Collisions", Beijing, 16-21 August 200

Effects of nuclear correlations on the 16^{16}O(e,e′pN)(e,e'pN) reactions to discrete final states

Calculations of the $^{16}$O$(e,e'pN)$ cross sections to the ground state and first excited levels of the $^{14}$C and $^{14}$N nuclei are presented. The effects of nuclear fragmentation have been obtained in a self-consistent approach and are accounted for in the determination of the two-nucleon removal amplitudes. The Hilbert space is partitioned in order to compute the contribution of both long- and short-range effects in a separate way. Both the two-proton and the proton-neutron emission cross sections have been computed within the same models for the reaction mechanism and the contribution from nuclear structure, with the aim of better comparing the differences between the two physical processes. The $^{16}$O$(e,e'pp)$ reaction is found to be sensitive to short-range correlations, in agreement with previous results. The $^{16}$O$(e,e'pn)$ cross section to $1^+$ final states is dominated by the $\Delta$ current and tensor correlations. For both reactions, the interplay between collective (long-range) effects and short-range and tensor correlations plays an important role. This suggests that the selectivity of $(e,e'pN)$ reactions to the final state can be used to probe correlations also beyond short-range effects.Comment: 13 pages, 9 figure

Transfer reactions and the dispersive optical-model

The dispersive optical-model is applied to transfer reactions. A systematic study of $(d,p)$ reactions on closed-shell nuclei using the finite-range adiabatic reaction model is performed at several beam energies and results are compared to data as well as to predictions using a standard global optical-potential. Overall, we find that the dispersive optical-model is able to describe the angular distributions as well as or better than the global parameterization. In addition, it also constrains the overlap function. Spectroscopic factors extracted using the dispersive optical-model are generally lower than those using standard parameters, exhibit a reduced dependence on beam energy, and are more in line with results obtained from $(e,e'p)$ measurements.Comment: Phys. Rev. C 84, 044611 (2011

Role of Long-Range Correlations on the Quenching of Spectroscopic Factors

We consider the proton and neutron quasiparticle orbits around the closed-shell 56Ni and 48Ca isotopes. It is found that large model spaces (beyond the capability of shell-model applications) are necessary for predicting the quenchings of spectroscopic factors. The particle-vibration coupling is identified as the principal mechanism. Additional correlations--due to configuration with several particle-hole excitations--are estimated using shell-model calculations and generate an extra reduction which is < ~4% for most quasiparticle states. The theoretical calculations nicely agree with (e,e'p) and heavy ion knock-out experiments. These results open a new path for a microscopic understanding of the shell-model.Comment: Minor comments added and typos corrected. Accepted for publication on Phys. Rev. Let

Spectroscopic Factors in 16O and Nucleon Asymmetry

The self-consistent Green's functions method is employed to study the spectroscopic factors of quasiparticle states around 16O, 28O, 40Ca and 60Ca. The Faddeev random phase approximation (FRPA) is used to account for the coupling of particles with collective excitation modes. Results for 16O are reviewed first. The same approach is applied to isotopes with large proton-neutron asymmetry to estimate its effect on spectroscopic factors. The results, based on the chiral N3LO force, exhibit an asymmetry dependence similar to that observed in heavy-ion knockout experiments but weaker in magnitude.Comment: Proceedings of the "KGU Yokohama Autumn School of Nuclear Physics", October 9-10, 200