Single particle spectrum and binding energy of nuclear matter

In non-relativistic Brueckner calculations of nuclear matter, the self-consistent single particle potential is strongly momentum dependent. To simplify the calculations, a parabolic approximation is often used in the literature. The variation in the binding energy value introduced by the parabolic approximation is quantitatively analyzed in detail. It is found that the approximation can introduce an uncertainty of 1-2 MeV near the saturation density.Comment: 6 Latex pages, 3 postscript figure

Study of refractive structure in the inelastic 16O+16O scattering at the incident energies of 250 to 1120 MeV

The data of inelastic 16O+16O scattering to the lowest 2+ and 3- excited states of 16O have been measured at Elab = 250, 350, 480, 704 and 1120 MeV and analyzed consistently in the distorted wave Born approximation (DWBA), using the semi- microscopic optical potentials and inelastic form factors given by the folding model, to reveal possible refractive structure of the nuclear rainbow that was identified earlier in the elastic 16O+16O scattering channel at the same energies. Given the known transition strengths of the 2+ and 3- states of 16O well determined from the (e,e') data, the DWBA description of the inelastic data over the whole angular range was possible only if the absorption in the exit channels is significantly increased (especially, for the 16O+16O(2+) exit channel). Although the refractive pattern of the inelastic 16O+16O scattering was found to be less pronounced compared to that observed in the elastic scattering channel, a clear remnant of the main rainbow maximum could still be seen in the inelastic cross section at Elab = 350 - 704 MeV.Comment: 26 pages, 10 figures, Accepted for publication in Nucl. Phys.

Missing monopole strength of the Hoyle state in the inelastic α\alpha+12^{12}C scattering

Analyses of the inelastic $\alpha$+$^{12}$C scattering at medium energies have indicated that the strength of the Hoyle state (the isoscalar 0$^+_2$ excitation at 7.65 MeV in $^{12}$C) seems to exhaust only 7 to 9% of the monopole energy weighted sum rule (EWSR), compared to about 15% of the EWSR extracted from inelastic electron scattering data. The full monopole transition strength predicted by realistic microscopic $\alpha$-cluster models of the Hoyle state can be shown to exhaust up to 22% of the EWSR. To explore the missing monopole strength in the inelastic $\alpha$+$^{12}$C scattering, we have performed a fully microscopic folding model analysis of the inelastic $\alpha$+$^{12}$C scattering at $E_{\rm lab}=104$ to 240 MeV using the 3-$\alpha$ resonating group wave function of the Hoyle state obtained by Kamimura, and a complex density-dependent M3Y interaction newly parametrized based on the Brueckner Hartree Fock results for nuclear matter. Our folding model analysis has shown consistently that the missing monopole strength of the Hoyle state is not associated with the uncertainties in the analysis of the $\alpha$+$^{12}$C scattering, but is most likely due to the short lifetime and weakly bound structure of this state which significantly enhances absorption in the exit $\alpha$+$^{12}$C$^*(0^+_2)$ channel.Comment: Accepted for publication in Physics Letters

Short-range correlations in asymmetric nuclear matter

The spectral function of protons in the asymmetric nuclear matter is calculated in the self-consistent T-matrix approach. The spectral function per proton increases with increasing asymmetry. This effect and the density dependence of the spectral function partially explain the observed increase of the spectral function with the mass number of the target nuclei in electron scattering experiments

Isospin dependence of nucleon effective mass in Dirac Brueckner-Hartree-Fock approach

The isospin dependence of the nucleon effective mass is investigated in the framework of the Dirac Brueckner-Hartree-Fock (DBHF) approach. The definition of nucleon scalar and vector effective masses in the relativistic approach is clarified. Only the vector effective mass is the quantity related to the empirical value extracted from the analysis in the nonrelatiistic shell and optical potentials. In the relativistic mean field theory, where the nucleon scalar and vector potentials are both energy independent, the neutron vector potential is stronger than that of proton in the neutron rich nuclear matter, which produces a smaller neutron vector effective mass than that of proton. It is pointed out that the energy dependence of nucleon potentials has to be considered in the analysis of the isospin dependence of the nucleon effective mass. In the DBHF the neutron vector effective mass is larger than that of proton once the energy dependence of nucleon potentials is considered. The results are consistent with the analysis of phenomenological isospin dependent optical potentials.Comment: 4 pages, 3 Postscript figure

Two-nucleon knockout contributions to the 12^{12}C(e,e′p)(e,e'p) reaction in the dip and {Δ\Delta}(1232) regions

The contributions from $^{12}$C$(e,e'pn)$ and $^{12}$C$(e,e'pp)$ to the semi-exclusive $^{12}$C$(e,e'p)$ cross section have been calculated in an unfactorized model for two-nucleon emission. We assume direct two-nucleon knockout after virtual photon coupling with the two-body pion-exchange currents in the target nucleus. Results are presented at several kinematical conditions in the dip and $\Delta$(1232) regions. The calculated two-nucleon knockout strength is observed to account for a large fraction of the measured $(e,e'p)$ strength above the two-nucleon emission threshold.Comment: 12 Revtex pages, 4 postscript figures (available upon request), University of Gent preprint SSF94-02-0

On the Dirac Structure of the Nucleon Selfenergy in Nuclear Matter

The relativistic structure of the self-energy of a nucleon in nuclear matter is investigated including the imaginary and real components which arise from the terms of first and second order in the NN interaction. A parameterized form of Brueckner $G$ matrix is used for the NN interaction. The effects of the terms beyond the DBHF approximation on quasiparticle energies and the optical potential for nucleon-nucleus scattering are discussed.Comment: 18 pages, Latex including 10 figures using psfi

Surface behaviour of the pairing gap in a slab of nuclear matter

The surface behaviour of the pairing gap previously studied for semi-infinite nuclear matter is analyzed in the slab geometry. The gap-shape function is calculated in two cases: (a) pairing with the Gogny force in a hard-wall potential and (b) pairing with the separable Paris interaction in a Saxon-Woods mean-field potential. It is shown that the surface features are preserved in the case of slab geometry, being almost independent of the width of the slab. It is also demonstrated that the surface enhancement is strengthened as the absolute value of chemical potential $|\mu|$ decreases which simulates the approach to the nucleon drip line.Comment: 12 pages, 2 figure

Modern nucleon-nucleon potentials and symmetry energy in infinite matter

We study the symmetry energy in infinite nuclear matter employing a non-relativistic Brueckner-Hartree-Fock approach and using various new nucleon-nucleon (NN) potentials, which fit np and pp scattering data very accurately. The potential models we employ are the recent versions of the Nijmegen group, Nijm-I, Nijm-II and Reid93, the Argonne $V_{18}$ potential and the CD-Bonn potential. All these potentials yield a symmetry energy which increases with density, resolving a discrepancy that existed for older NN potentials. The origin of remaining differences is discussed.Comment: 17 pages, 10 figures included, elsevier latex style epsart.st

Effective mass splitting of neutron and proton and isospin emission in heavy-ion collisions

Within the framework of an isospin and momentum dependent transport model, the emissions of isospin particles (nucleons and light clusters) squeezed out in heavy-ion collisions are investigated as probes of the poorly known symmetry energy at high baryon density. Two different mass splittings of neutrons and protons in nuclear medium as $m_{n}^{\ast}>m_{p}^{\ast}$ and $m_{n}^{\ast}<m_{p}^{\ast}$ are used in the model and their influence on the isospin emission in heavy-ion collisions is discussed thoroughly. The competition between the stiffness and the momentum dependence of the symmetry potential on reaction dynamics are compared and systematically analyzed. It is found that the difference of the neutron and proton directed flows and the transverse momentum distribution of the neutron/proton ratio are sensitive to the stiffness of the symmetry energy, which can not be changed with the controversial effective mass splitting. The elliptic flows of free nucleons at high transverse momentum within mid-rapidity emission are a promising observable as distinguishing the nucleon effective mass splitting.Comment: 16 pages, 7 figure