Asymmetry dependence of proton correlations.

Department of Chemistry, Washington University, St Louis, MO 63130, USA.
Physical Review Letters (Impact Factor: 7.73). 11/2006; 97(16):162503. DOI: 10.1103/PHYSREVLETT.97.162503
Source: PubMed

ABSTRACT 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.

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    ABSTRACT: The effects of short-range correlations on the nucleon self-energy in $^{40}$Ca are investigated using the charge-dependent Bonn (CDBonn) interaction. Comparisons are made with recent results for the self-energy of $^{40}$Ca derived from the dispersive optical-model (DOM). Particular emphasis is placed on the non-locality of the imaginary part of the microscopic self-energy which suggests that future DOM analyses should include this feature. In particular, data below the Fermi energy appear sensitive to the implied orbital angular momentum dependence of the self-energy. Quasiparticle properties obtained for the CDBonn interaction are substantially more mean-field-like than the corresponding DOM results with spectroscopic factors larger by about 0.2 e.g. Reaction cross sections obtained from the microscopic self-energy for scattering energies up to 100 MeV indicate that an adequate description of volume absorption is obtained while a considerable fraction of surface absorption is missing. The analysis of the non-locality of the imaginary part of the microscopic self-energy suggests that a simple gaussian provides an adequate description, albeit with rather large values for $\beta$, the non-locality parameter.
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    ABSTRACT: Neutron elastic-scattering angular distributions were measured at beam energies of 11.9 and 16.9 MeV on 40,48Ca targets. These data plus other elastic-scattering measurements, total and reaction cross-sections measurements, (e,e′p) data, and single-particle energies for magic and doubly magic nuclei have been analyzed in the dispersive optical-model (DOM), generating nucleon self-energies (optical-model potentials) that can be related, via the many-body Dyson equation, to spectroscopic factors and occupation probabilities. It is found that, for stable nuclei with N⩾Z, the imaginary surface potential for protons exhibits a strong dependence on the neutron-proton asymmetry. This result leads to a more modest dependence of the spectroscopic factors on asymmetry. The measured data and the DOM analysis of all considered nuclei clearly demonstrate that the neutron imaginary surface potential displays very little dependence on the neutron-proton asymmetry for nuclei near stability (N⩾Z).
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