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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

In-medium effects on K{sup 0} mesons in relativistic heavy-ion collisions

We present the transverse momentum spectra and rapidity distributions of {pi}{sup -} and K{sub S}{sup 0} in Ar + KCl reactions at a beam kinetic energy of 1.756 A GeV measured with the High Acceptance Di-Electron Spectrometer (HADES). The reconstructed K{sub S}{sup 0} sample is characterized by good event statistics for a wide range in momentum and rapidity. We compare the experimental {pi}{sup -} and K{sub S}{sup 0} distributions to predictions by the Isospin Quantum Molecular Dynamics (IQMD) model. The model calculations show that K{sub S}{sup 0} at low transverse momenta constitute a particularly well-suited tool to investigate the kaon in-medium potential. Our K{sub S}{sup 0} data suggest a strong repulsive in-medium K{sup 0} potential of about 40 MeV strength.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

New parametrization for the nuclear covariant energy density functional with a point-coupling interaction

A new parametrization PC-PK1 for the nuclear covariant energy density functional with nonlinear point-coupling interaction is proposed by fitting to observables of 60 selected spherical nuclei, including the binding energies, charge radii, and empirical pairing gaps. The success of PC-PK1 is illustrated in the description of infinite nuclear matter and finite nuclei including the ground-state and low-lying excited states. In particular, PC-PK1 provides a good description for the isospin dependence of binding energy along either the isotopic or the isotonic chain, which makes it reliable for application in exotic nuclei. The predictive power of PC-PK1 is also illustrated for the nuclear low-lying excitation states in a five-dimensional collective Hamiltonian in which the parameters are determined by constrained calculations for triaxial shapes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Symmetry energy, its density slope, and neutron-proton effective mass splitting at normal density extracted from global nucleon optical potentials

Based on the Hugenholtz-Van Hove theorem, it is shown that both the symmetry energy E{sub sym}({rho}) and its density slope L({rho}) at normal density {rho}{sub 0} are completely determined by the nucleon global optical potentials. The latter can be extracted directly from nucleon-nucleus scatterings, (p,n) charge-exchange reactions, and single-particle energy levels of bound states. Averaging all phenomenological isovector nucleon potentials constrained by world data available in the literature since 1969, the best estimates of E{sub sym}({rho}{sub 0})=31.3 MeV and L({rho}{sub 0})=52.7 MeV are simultaneously obtained. Moreover, the corresponding neutron-proton effective mass splitting in neutron-rich matter of isospin asymmetry {delta} is estimated to be (m{sub n}{sup *}-m{sub p}{sup *})/m=0.32{delta}.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Fragmentation paths in dynamical models

We undertake a quantitative comparison of multifragmentation reactions, as modeled by two different approaches: the antisymmetrized molecular dynamics (AMD) and the momentum-dependent stochastic mean-field (SMF) model. Fragment observables and pre-equilibrium (nucleon and light cluster) emission are analyzed, in connection with the underlying compression-expansion dynamics in each model. Considering reactions between neutron-rich systems, observables related to the isotopic properties of emitted particles and fragments are also discussed, as a function of the parametrization employed for the isovector part of the nuclear interaction. We find that the reaction path, particularly the mechanism of fragmentation, is different in the two models and reflects on some properties of the reaction products, including their isospin content. This should be taken into account in the study of the density dependence of the symmetry energy from such collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Dynamics of strangeness production in heavy-ion collisions near threshold energies

Within the framework of the improved isospin-dependent quantum molecular dynamics (ImIQMD) model, the dynamics of strangeness (K{sup 0,+}, {Lambda}, and {Sigma}{sup -,0,+}) production in heavy-ion collisions near threshold energies is investigated systematically, with the strange particles considered to be produced mainly by inelastic collisions of baryon-baryon and pion-baryon. Collisions in the region of suprasaturation densities of the dense baryonic matter formed in heavy-ion collisions dominate the yields of strangeness production. Total multiplicities as functions of incident energies and collision centralities are calculated with the Skyrme parameter SLy6. The excitation function of strangeness production is analyzed and also compared with the KaoS data for K{sup +} production in the reactions {sup 12}C+{sup 12}C and {sup 197}Au+{sup 197}Au.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Flavor asymmetry of sea quarks in the unquenched quark model

The flavor asymmetry of the nucleon sea is studied in the framework of the unquenched quark model in which the effects of quark-antiquark pairs (uu-bar, dd-bar, and ss-bar) are taken into account via a microscopic, QCD-inspired, quark-antiquark creation mechanism. The inclusion of the qq-bar pairs leads to an excess of d-bar over u-bar, in agreement with the experimental data for the proton. In addition, the results for the flavor asymmetry of all ground-state octet and decuplet baryons are presented. The isospin symmetry leads to simple relations among the flavor asymmetries of octet and decuplet baryons. The flavor asymmetry of the {Sigma}{sup +} hyperon is predicted to be very similar to that of the proton and much larger than that for the {Xi}{sup 0} hyperon. A comparison with other approaches shows large differences in the predictions for the flavor asymmetries of the hyperons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Effects of elastic and inelastic NN scattering cross sections on {pi}{sup -}/{pi}{sup +} ratios in heavy-ion collisions at intermediate energies

Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model and the scaling model according to nucleon effective mass, effects of elastic and inelastic NN scattering cross sections on {pi}{sup -}/{pi}{sup +} in the neutron-rich reaction of {sup 48}Ca+{sup 48}Ca at a beam energy of 400 MeV/nucleon are studied. It is found that cross-section effects of both NN elastic and inelastic scatterings affect {Delta}{sub 1232}, {pi}{sup -} and {pi}{sup +} production, as well as the value of {pi}{sup -}/{pi}{sup +}.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Spin-orbit and orbit-orbit strengths for the radioactive neutron-rich doubly magic nucleus {sup 132}Sn in relativistic mean-field theory

Relativistic mean-field (RMF) theory is applied to investigate the properties of the radioactive neutron-rich doubly magic nucleus {sup 132}Sn and the corresponding isotopes and isotones. The two-neutron and two-proton separation energies are well reproduced by the RMF theory. In particular, the RMF results agree with the experimental single-particle spectrum in {sup 132}Sn as well as the Nilsson spin-orbit parameter C and orbit-orbit parameter D thus extracted, but remarkably differ from the traditional Nilsson parameters. Furthermore, the present results provide a guideline for the isospin dependence of the Nilsson parameters.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Multifragmentation around the transition energy in intermediate-energy heavy-ion collisions

Fragmentation of light charged particles is studied for various systems at different incident energies between 50 and 1000 MeV/nucleon. We analyze fragment production at the incident energies below, at, and above the transition energies using the isospin-dependent quantum molecular dynamics model. The trends observed for the fragment production and rapidity distributions depend upon the incident energy, size of the fragments, and composite mass of the reacting system, as well as on the impact parameter of the reaction. The free nucleons and light charged particles show continuous homogeneous changes, irrespective of the transition energies, indicating that there is no relation between the transition energy and production of the free as well as light charged particles.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Gluon condensate in a pion superfluid beyond the mean-field approximation

We study gluon condensate in a pion superfluid by calculating the equation of state of the system in the Nambu-Jona-Lasinio model. While in mean-field approximation the growing pion condensate leads to an increasing gluon condensate, meson fluctuations reduce the gluon condensate, and the broken scalar symmetry can be smoothly restored at finite isospin density.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Gamow-Teller strength distributions for {beta}{beta}-decaying nuclei within continuum quasiparticle random-phase approximation

An isospin-self-consistent pn-continuum-QRPA approach is formulated and applied to describe the Gamow-Teller strength distributions for {beta}{beta}-decaying open-shell nuclei. Calculation results obtained for the pairs of nuclei {sup 76}Ge-Se, {sup 100}Mo-Ru, {sup 116}Cd-Sn, and {sup 130}Te-Xe are compared with available experimental data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Born term of the {pi}N scattering amplitude in the Skyrme model

The Skyrme model is applied to the study of the {pi}N scattering amplitude. The useful expression of amplitude given by the chiral reduction formula is employed. The calculation is performed in the lowest order of 1/N{sub c}: a source of interaction is a classical soliton taking a hedgehog configuration. It is important to consider the zero modes both for the translation invariance and for the isospin symmetry simultaneously. Despite the former negative impression, the Skyrme model correctly produces the Born term in the scattering amplitude.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Mean-field approach to flavor susceptibilities with a vector interaction

We show that flavor-diagonal and off-diagonal susceptibilities of light quarks at vanishing chemical potential can be calculated consistently assuming the baryon density and isospin density dependence of QCD to be expressed by a vector-isoscalar and a vector-isovector coupling, respectively. At the mean-field level, their expression depends only on the effective medium-dependent couplings and quark thermodynamic potential. The strength of the couplings can be then estimated from the model using lattice QCD data as an input.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Energy release from hadron-quark phase transition in neutron stars and the axial w mode of gravitational waves

Describing the hyperonic and quark phases of neutron stars with an isospin- and momentum-dependent effective interaction for the baryon octet and the MIT bag model, respectively, and using the Gibbs conditions to construct the mixed phase, we study the energy release from a neutron star owing to the hadron-quark phase transition. Moreover, the frequency and damping time of the first axial w mode of gravitational waves are studied for both hyperonic and hybrid stars. We find that the energy release is much more sensitive to the bag constant than the density dependence of the nuclear symmetry energy. Also, the frequency of the w mode is found to be significantly different with or without the hadron-quark phase transition and depends strongly on the value of the bag constant. Effects of the density dependence of the nuclear symmetry energy become, however, important for large values of the bag constant that lead to higher hadron-quark transition densities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Core-crust transition in neutron stars: Predictivity of density developments

The possibility to draw links between the isospin properties of nuclei and the structure of compact stars is a stimulating perspective. In order to pursue this objective on a sound basis, the correlations from which such links can be deduced have to be carefully checked against model dependence. Using a variety of nuclear effective models and a microscopic approach, we study the relation between the predictions of a given model and those of a Taylor density development of the corresponding equation of state: this establishes to what extent a limited set of phenomenological constraints can determine the core-crust transition properties. From a correlation analysis, we show that (a) the transition density {rho}{sub t} is mainly correlated with the symmetry energy slope L, (b) the proton fraction Y{sub p,t} with the symmetry energy and symmetry energy slope (J,L) defined at saturation density, or, even better, with the same quantities defined at {rho}=0.1 fm{sup -3}, and (c) the transition pressure P{sub t} with the symmetry energy slope and curvature (L,K{sub sym}) defined at {rho}=0.1 fm{sup -3}.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Effect of the momentum dependence of the nuclear symmetry potential on the {pi}{sup -}/{pi}{sup +} ratio in heavy-ion collisions

In the framework of the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model, the effect of the momentum dependence of the nuclear symmetry potential on the {pi}{sup -}/{pi}{sup +} ratio in the neutron-rich reaction {sup 132}Sn +{sup 124}Sn at a beam energy of 400 MeV/nucleon is studied. We find that the momentum dependence of the nuclear symmetry potential affects the compressed density of colliding nuclei, the numbers of produced {pi}{sup -} and {pi}{sup +}, as well as the value of the {pi}{sup -}/{pi}{sup +} ratio. The momentum-dependent nuclear symmetry potential increases the compressed density of colliding nuclei, the number of produced resonances {Delta}(1232), N{sup *}(1440), {pi}{sup -}, and {pi}{sup +}, as well as the value of the {pi}{sup -}/{pi}{sup +} ratio.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Photo- and electroproduction of K{sup 0{Lambda}} near threshold and effects of the K{sup 0} electromagnetic form factor

By extending our previous isobar model to the K{sup 0{Lambda}} isospin channel, we investigate the properties of the K{sup 0{Lambda}} photo- and electroproduction at energies near threshold. It is found that the pseudovector coupling yields significantly larger cross sections. Variation of the K{sub 1} coupling constants has significant effect only on the pseudovector model. The electromagnetic form factor of the neutral kaon K{sup 0} is found to have a sizable effect on the longitudinal cross section of the K{sup 0{Lambda}} electroproduction near the threshold.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Gamow-Teller unit cross sections for (t,{sup 3}He) and ({sup 3}He,t) reactions

The proportionality between differential cross sections at vanishing linear momentum transfer and Gamow-Teller transition strength, expressed in terms of the unit cross section ({sigma}{sub GT}), was studied as a function of target mass number for (t,{sup 3}He) and ({sup 3}He,t) reactions at 115A MeV and 140A MeV, respectively. Existing ({sup 3}He,t) and (t,{sup 3}He) data on targets with mass number 12{<=}A{<=}120 were complemented with new and reevaluated (t,{sup 3}He) data on proton, deuteron, {sup 6}Li, and {sup 12}C targets. It was found that in spite of the small difference in beam energies between the two probes, the unit cross sections have a nearly identical and simple dependence on target mass number A, for A{>=}12: {sigma}{sub GT}=109/A{sup 0.65}. The factorization of the unit cross sections in terms of a kinematical factor, a distortion factor, and the strength of the effective spin-isospin transfer nucleus-nucleus interaction was investigated. Simple phenomenological functions depending on mass number A were extracted for the latter two. By comparison with plane and distorted-wave Born approximation calculations, it was found that the use of a short-range approximation for knock-on exchange contributions to the transition amplitude results in overestimated cross sections for reactions involving the composite ({sup 3}He,t) and (t,{sup 3}He) probes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗