39 research outputs found
Antiproton-nucleus potentials from global fits to antiprotonic X-rays and radiochemical data
We report on global fits of optical-model parameters to 90 data points for
X-rays and 17 data points of radiochemical data put together. With the
help of separate fits to the two kinds of data it is possible to determine
phenomenologically the radial region where the absorption of antiprotons takes
place and to obtain neutron densities which represent the average behaviour
over the periodic table. A finite-range attractive and absorptive -nuclear isoscalar potential fits the data well. Self-consistent dynamical
calculations within the RMF model demonstrate that the polarization of the
nucleus by the {\it atomic} antiproton is negligible.Comment: 18 pages, 6 figures, one table. Extended discussion, to appear in
Nucl. Phys.
Renormalization of the isovector amplitude in pionic atoms
The extraction of the isovector s-wave pi N amplitude from pionic atoms is
studied with special emphasis on uncertainties and their dependence on the
assumptions made regarding the neutron density distributions in nuclei and on
the size of the data base used . Only `global' analyses of pionic-atom data
reveal a discrepancy between the extracted isovector s-wave pi N amplitude
b_1=-0.108\pm0.007 m_\pi^{-1} and its free pi N counterpart
b_1^{free}=-0.0885^{+0.0010}_{-0.0021} m_\pi ^{-1}, where the uncertainty in
the neutron densities is included in the error analysis. The role of `deeply
bound' pionic atom states is discussed and the reason for failure of these
states to provide new information is explained.Comment: 17 pages, 4 figures, slightly extended, accepted by NP
High-Energy Approach for Heavy-Ion Scattering with Excitations of Nuclear Collective States
A phenomenological optical potential is generalized to include the Coulomb
and nuclear interactions caused by the dynamical deformation of its surface. In
the high-energy approach analytical expressions for elastic and inelastic
scattering amplitudes are obtained where all the orders in the deformation
parameters are included. The multistep effect of the 2 rotational state
excitation on elastic scattering is analyzed. Calculations of inelastic cross
sections for the O ions scattered on different nuclei at about hundred
Mev/nucleon are compared with experimental data, and important role of the
Coulomb excitation is established.Comment: 9 pages; 3 figures. Submitted to the Physics of Atomic Nucle
Deformation of Nuclei Close to the Two-Neutron Drip Line in Mg Region
We perform the Hartree-Fock-Bogoliubov (HFB) calculations for ground states
of even Mg isotopes using the Skyrme force and a density-dependent zero-range
pairing force. The HFB equation is solved in a three-dimensional cartesian
mesh, and a convergence of deformation is carefully examined with respect to a
cut-off radius for a check of the calculations. We discuss systematics of the
two-neutron separation energy, deformation and root-mean-square radius. We have
found that 36,38,40Mg have appreciable static deformation, where 40Mg is a
two-neutron drip-line nucleus in our calculation, and the deformations of the
neutron and proton are different in these three nuclei. The deformation
property is analyzed on the basis of the single-particle diagram. It is shown
that N=28 is not a closed shell in Mg as well as Si.Comment: 13 pages, 8 Postscript figures, submitted to Nucl.Phy
Constraining the Radii of Neutron Stars with Terrestrial Nuclear Laboratory Data
Neutron star radii are primarily determined by the pressure of isospin
asymmetric matter which is proportional to the slope of the nuclear symmetry
energy. Available terrestrial laboratory data on the isospin diffusion in
heavy-ion reactions at intermediate energies constrain the slope of the
symmetry energy. Using this constraint, we show that the radius (radiation
radius) of a 1.4 solar mass neutron star is between 11.5 (14.4) and 13.6 (16.3)
km.Comment: 11 pages, 3 figures; version to be published in Phys. Lett.
Relativistic nuclear model with point-couplings constrained by QCD and chiral symmetry
We derive a microscopic relativistic point-coupling model of nuclear
many-body dynamics constrained by in-medium QCD sum rules and chiral symmetry.
The effective Lagrangian is characterized by density dependent coupling
strengths, determined by chiral one- and two-pion exchange and by QCD sum rule
constraints for the large isoscalar nucleon self-energies that arise through
changes of the quark condensate and the quark density at finite baryon density.
This approach is tested in the analysis of the equations of state for symmetric
and asymmetric nuclear matter, and of bulk and single-nucleon properties of
finite nuclei. In comparison with purely phenomenological mean-field
approaches, the built-in QCD constraints and the explicit treatment of pion
exchange restrict the freedom in adjusting parameters and functional forms of
density dependent couplings. It is shown that chiral (two-pion exchange)
fluctuations play a prominent role for nuclear binding and saturation, whereas
strong scalar and vector fields of about equal magnitude and opposite sign,
induced by changes of the QCD vacuum in the presence of baryonic matter,
generate the large effective spin-orbit potential in finite nuclei.Comment: 46 pages, 12 figures, uses elsart.cls, revised version, to appear in
Nucl.Phys. A735 (2004) 449-48
The effective force NL3 revisited
Covariant density functional theory based on the relativistic mean field
(RMF) Lagrangian with the parameter set NL3 has been used in the last ten years
with great success. Now we propose a modification of this parameter set, which
improves the description of the ground state properties of many nuclei and
simultaneously provides an excellent description of excited states with
collective character in spherical as well as in deformed nuclei.Comment: 8 pages, 5 figure
A microscopic estimate of the nuclear matter compressibility and symmetry energy in relativistic mean-field models
The relativistic mean-field plus RPA calculations, based on effective
Lagrangians with density-dependent meson-nucleon vertex functions, are employed
in a microscopic analysis of the nuclear matter compressibility and symmetry
energy. We compute the isoscalar monopole and the isovector dipole response of
Pb, as well as the differences between the neutron and proton radii for
Pb and several Sn isotopes. The comparison of the calculated excitation
energies with the experimental data on the giant monopole resonance in
Pb, restricts the nuclear matter compression modulus of structure
models based on the relativistic mean-field approximation to MeV. The isovector giant dipole resonance in Pb, and the
available data on differences between neutron and proton radii, limit the range
of the nuclear matter symmetry energy at saturation (volume asymmetry) to 32
MeV 36 MeV.Comment: 16 pages, 6 figure
Relativistic nuclear energy density functional constrained by low-energy QCD
A relativistic nuclear energy density functional is developed, guided by two
important features that establish connections with chiral dynamics and the
symmetry breaking pattern of low-energy QCD: a) strong scalar and vector fields
related to in-medium changes of QCD vacuum condensates; b) the long- and
intermediate-range interactions generated by one-and two-pion exchange, derived
from in-medium chiral perturbation theory, with explicit inclusion of
excitations. Applications are presented for binding energies,
radii of proton and neutron distributions and other observables over a wide
range of spherical and deformed nuclei from to . Isotopic
chains of and nuclei are studied as test cases for the isospin
dependence of the underlying interactions. The results are at the same level of
quantitative comparison with data as the best phenomenological relativistic
mean-field models.Comment: 48 pages, 12 figures, elsart.cls class file. Revised version,
accepted for publication in Nucl. Phys.
Relativistic Random-Phase Approximation with density-dependent meson-nucleon couplings
The matrix equations of the relativistic random-phase approximation (RRPA)
are derived for an effective Lagrangian characterized by density-dependent
meson-nucleon vertex functions. The explicit density dependence of the
meson-nucleon couplings introduces rearrangement terms in the residual two-body
interaction, that are essential for a quantitative description of excited
states. Illustrative calculations of the isoscalar monopole, isovector dipole
and isoscalar quadrupole response of Pb, are performed in the fully
self-consistent RRPA framework, based on effective interactions with a
phenomenological density dependence adjusted to nuclear matter and ground-state
properties of spherical nuclei. The comparison of the RRPA results on multipole
giant resonances with experimental data constrains the parameters that
characterize the isoscalar and isovector channel of the density-dependent
effective interactions.Comment: RevTeX, 8 eps figures, submitted to Phys. Rev.