Showing papers in "Physical Review C in 1995"
TL;DR: The authors present a new high-quality nucleon-nucleon potential with explicit charge dependence and charge asymmetry, which they designate Argonne {upsilon}{sub 18}.
Abstract: The authors present a new high-quality nucleon-nucleon potential with explicit charge dependence and charge asymmetry, which they designate Argonne {upsilon}{sub 18}. The model has a charge-independent part with fourteen operator components that is an updated version of the Argonne {upsilon}{sub 14} potential. Three additional charge-dependent and one charge-asymmetric operators are added, along with a complete electromagnetic interaction. The potential has been fit directly to the Nijmegen pp and np scattering data base, low-energy nn scattering parameters, and deuteron binding energy. With 40 adjustable parameters it gives a {chi}{sup 2} per datum of 1.09 for 4,301 pp and np data in the range 0--350 MeV.
2,409 citations
TL;DR: The Bethe-Weizsaecker formula is shown to be the asymptotic limit of the present one(s), and the surface energy of nuclear matter turns out to be probably smaller than currently accepted.
Abstract: By assuming the existence of a pseudopotential smooth enough to do Hartree-Fock variations and good enough to describe nuclear structure, we construct mass formulas that rely on general scaling arguments and on a schematic reading of shell model calculations. Fits to 1751 known binding energies for N,Z\ensuremath{\ge}8 lead to rms errors of 375 keV with 28 parameters. Tests of the extrapolation properties are passed successfully. The Bethe-Weizs\"acker formula is shown to be the asymptotic limit of the present one(s). The surface energy of nuclear matter turns out to be probably smaller than currently accepted.
422 citations
TL;DR: A relativistic mean-field model of nuclear matter with arbitrary proton fraction is studied at finite temperature and the Maxwell construction through the phase-separation region is discussed, and it is shown that the stable configuration can be determined uniquely at every density.
Abstract: A relativistic mean-field model of nuclear matter with arbitrary proton fraction is studied at finite temperature. An analysis is performed of the liquid-gas phase transition in a system with two conserved charges (baryon number and isospin) using the stability conditions on the free energy, the conservation laws, and Gibbs' criteria for phase equilibrium. For a binary system with two phases, the coexistence surface (binodal) is two dimensional. The Maxwell construction through the phase-separation region is discussed, and it is shown that the stable configuration can be determined uniquely at every density. Moreover, because of the greater dimensionality of the binodal surface, the liquid-gas phase transition is continuous (second order by Ehrenfest's definition), rather than discontinuous (first order), as in familiar one-component systems. Using a mean-field equation of state calibrated to the properties of nuclear matter and finite nuclei, various phase-separation scenarios are considered. The model is then applied to the liquid-gas phase transition that may occur in the warm, dilute matter produced in energetic heavy-ion collisions. In asymmetric matter, instabilities that produce a liquid-gas phase separation arise from fluctuations in the proton concentration (chemical instability), rather than from fluctuations in the baryon density (mechanical instability).
373 citations
TL;DR: A newly developed relativistic transport model for high energy heavy-ion collisions shows that in central collisions there exists a large volume of sufficiently long-lived superdenseHadronic matter whose local baryon and energy densities exceed the critical densities for the hadronic matter to quark-gluon plasma transition.
Abstract: We present the detail of a newly developed relativistic transport model (ART 1.0) for high energy heavy-ion collisions. Using this model, we first study the general collision dynamics between heavy ions at the AGS energies. We then show that in central collisions there exists a large volume of sufficiently long-lived superdense hadronic matter whose local baryon and energy densities exceed the critical densities for the hadronic matter to quark-gluon plasma transition. The size and lifetime of this matter are found to depend strongly on the equation of state. We also investigate the degree and time scale of thermalization as well as the radial flow during the expansion of the superdense hadronic matter. The flow velocity profile and the temperature of the hadronic matter at freeze-out are extracted. The transverse momentum and rapidity distributions of protons, pions, and kaons calculated with and without the mean field are compared with each other and also with the preliminary data from the E866/E802 Collaboration to search for experimental observables that are sensitive to the equation of state. It is found that these inclusive, single particle observables depend weakly on the equation of state. The difference between results obtained with and without the nuclear mean field is only about 20%. The baryon transverse collective flow in the reaction plane is also analyzed. It is shown that both the flow parameter and the strength of the ``bounce-off'' effect are very sensitive to the equation of state. In particular, a soft equation of state with a compressibility of 200 MeV results in an increase of the flow parameter by a factor of 2.5 compared to the cascade case without the mean field. This large effect makes it possible to distinguish the predictions from different theoretical models and to detect the signatures of the quark-gluon plasma which is expected to significantly soften the equation of state.
336 citations
TL;DR: A model based on quantum molecular dynamics incorporated with a statistical decay model (SDM) to describe various nuclear reactions in a unified way is proposed and a unified description of the three major reaction mechanisms, i.e., compound, preequilibrium, and spallation processes, is given.
Abstract: We propose a model based on quantum molecular dynamics (QMD) incorporated with a statistical decay model (SDM) to describe various nuclear reactions in a unified way. In this first part of the work, the basic ingredients of the model are defined and the model is applied systematically to the nucleon- (N-)induced reactions. It has been found that our model can give a remarkable agreement in the energy-angle double differential cross sections of (N,${\mathit{xN}}^{\ensuremath{'}}$) type reactions for incident energies from 100 MeV to 3 GeV with a fixed parameter set. A unified description of the three major reaction mechanisms of (N,${\mathit{xN}}^{\ensuremath{'}}$) reactions, i.e., compound, preequilibrium, and spallation processes, is given with our model.
316 citations
TL;DR: In this article, the trial wave functions are chosen to be combinations of correlated Gaussians, which are constructed from products of the singleparticle Gaussian wave packets through an integral transformation, thereby facilitating fully analytical calculations of the matrix elements.
Abstract: Precise variational solutions are given for problems involving diverse fermionic and bosonic (N=2--7)-body systems. The trial wave functions are chosen to be combinations of correlated Gaussians, which are constructed from products of the single-particle Gaussian wave packets through an integral transformation, thereby facilitating fully analytical calculations of the matrix elements. The nonlinear parameters of the trial function are chosen by a stochastic technique. The method has proved very efficient, virtually exact, and it seems feasible for any few-body bound-state problems emerging in nuclear or atomic physics.
297 citations
TL;DR: The paper reviews string fusion into color ropes and hadronic rescattering which serve as models for these interactions for collective interactions in the preequilibrium quark matter andHadronic resonance gas stage of ultrarelativistic nucleus-nucleus collisions.
Abstract: Collective interactions in the preequilibrium quark matter and hadronic resonance gas stage of ultrarelativistic nucleus-nucleus collisions are studied in the framework of the transport theoretical approach RQMD. The paper reviews string fusion into color ropes and hadronic rescattering which serve as models for these interactions. Hadron production in central Pb(160A GeV) on Pb collisions has been calculated. The changes of the final flavor composition are more pronounced than in previous RQMD studies of light ion induced reactions at 200A GeV. The ratio of created quark pairs ss\ifmmode\bar\else\textasciimacron\fi{}/(u\ifmmode \bar{u}\else \={u}\fi{}+dd\ifmmode\bar\else\textasciimacron\fi{}) is enhanced by a factor of 2.4 in comparison to pp results. Color rope formation increases the initially produced antibaryons to 3 times the value in the ``NN mode,'' but only one quarter of the produced antibaryons survives because of subsequent strong absorption. The differences in the final particle composition for Pb on Pb collisions compared to S-induced reactions are attributed to the hadronic resonance gas stage which is baryon-richer and lasts longer.
289 citations
TL;DR: Spontaneous-fission half-lives of the heaviest nuclei are analyzed in a multidimensional deformation space and are predicted for many unknown nuclei, sufficient to detect them if synthesized in a laboratory.
Abstract: Spontaneous-fission half-lives of the heaviest nuclei are analyzed in a multidimensional deformation space. They are calculated in a dynamical approach, without any adjustable parameters. The potential energy is obtained by the macroscopic-microscopic method and the inertia tensor by the cranking method. The action integral is minimized by a variational procedure. Even-even nuclei with proton number {ital Z}=104--114 and neutron number {ital N}=142--176 are considered. The results reproduce existing experimental data rather well. Relatively long half-lives are predicted for many unknown nuclei, sufficient to detect them if synthesized in a laboratory.
256 citations
TL;DR: In this representation it is clearly seen that the excitation functions are not smooth and featureless; each is unique and is shown to depend on the details of the structure of the interacting nuclei.
Abstract: Fusion excitation functions for the reactions $^{144,148,154}\mathrm{Sm}$ and $^{186}\mathrm{W}$ + $^{16}\mathrm{O}$ and $^{144}\mathrm{Sm}$ + $^{17}\mathrm{O}$ have been measured with high precision, both in the cross sections and the small energy intervals, thus allowing meaningful fusion barrier distributions to be extracted. In this representation it is clearly seen that the excitation functions are not smooth and featureless; each is unique and is shown to depend on the details of the structure of the interacting nuclei. The effects of excitation of the collective single phonon states in $^{144}\mathrm{Sm}$ are evident. For the $^{17}\mathrm{O}$ projectile, the role of additional coupling to neutron stripping channels with positive Q values can be seen. As expected, the barrier distributions associated with $^{154}\mathrm{Sm}$ and $^{186}\mathrm{W}$ are dominated by deformation effects. However, the data appear to display sensitivity to additional couplings, even though they involve relatively weak inelastic and transfer channels.
251 citations
TL;DR: A fully covariant approach to a density dependent hadron field theory is presented and results from Hartree calculations for energy spectra, binding energies, and charge density distributions of {sup 16}O, {sup 40,48}Ca, and {sup 208}Pb are presented.
Abstract: A fully covariant approach to a density dependent hadron field theory is presented. The relation between in-medium NN interactions and field-theoretical meson-nucleon vertices is discussed. The medium dependence of nuclear interactions is described by a functional dependence of the meson-nucleon vertices on the baryon field operators. As a consequence, the Euler-Lagrange equations lead to baryon rearrangement self-energies which are not obtained when only a parametric dependence of the vertices on the density is assumed. It is shown that the approach is energy-momentum conserving and thermodynamically consistent. Solutions of the field equations are studied in the mean-field approximation. Descriptions of the medium dependence in terms of the baryon scalar and vector density are investigated. Applications to infinite nuclear matter and finite nuclei are discussed. Density dependent coupling constants obtained from Dirac-Brueckner calculations with the Bonn NN potentials are used. Results from Hartree calculations for energy spectra, binding energies, and charge density distributions of $^{16}\mathrm{O}$, $^{40,48}\mathrm{Ca}$, and $^{208}\mathrm{Pb}$ are presented. Comparisons to data strongly support the importance of rearrangement in a relativistic density dependent field theory. Most striking is the simultaneous improvement of charge radii, charge densities, and binding energies. The results indicate the appearance of a new ``Coester line'' in the nuclear matter equation of state.
216 citations
TL;DR: The calculated magnetic moments describe the observed data quite well, and the neutron number dependence of the observed magnetic moments is explained as the reflection of the structure change of the isotopes from the clustering structure to the shell-model-like structure.
Abstract: Structure of odd-even and even-even isotopes of Li and Be is studied systematically with antisymmetrized molecular dynamics which is a theoretical method free from any model assumptions such as the existence of clustering. The construction of energy-minimum intrinsic states with definite parity is made by the use of the frictional cooling method. Angular momentum projection is applied to these intrinsic states in order to obtain the eigenstates of angular momentum. It is shown that the clustering structure appears in the nuclei in the {ital N}{approx}{ital Z} region with {ital N} and {ital Z} standing for the neutron and proton numbers, respectively. The clustering structure changes toward the shell-model-like structure as {ital N} increases to around {ital N}{approx}8. Furthermore appearance of new-type clustering features is suggested in the neutron-richer region with {ital N}{gt}8. Energy spectra and other quantities are shown to be reproduced well. Especially the calculated magnetic moments describe the observed data quite well, and the neutron number dependence of the observed magnetic moments is explained as the reflection of the structure change of the isotopes from the clustering structure to the shell-model-like structure. It is indicated that the density dependence of the effective interaction is important.
TL;DR: This is the first set of resonance parameters from a VPI analysis constrained by fixed-{ital t} dispersion relations, finding candidates in the {ital S}{sub 11} and {ital F}{sub 15} partial-wave amplitudes.
Abstract: We present the results of energy-dependent and single-energy partial-wave analyses of {pi}{ital N} elastic scattering data with laboratory kinetic energies below 2.1 GeV. Resonance structures have been extracted using Breit-Wigner fits, speed plots, and a complex plane mapping of the associated poles and zeros. This is the first set of resonance parameters from a VPI analysis constrained by fixed-{ital t} dispersion relations. We have searched our solutions for structures which may have been missed in our previous analyses, finding candidates in the {ital S}{sub 11} and {ital F}{sub 15} partial-wave amplitudes. Our results are compared with those found by the Karlsruhe, Carnegie-Mellon--Berkeley, and Kent State groups.
TL;DR: Rotation-induced time-odd components in the nuclear mean field are analyzed using the Hartree-Fock cranking approach with effective interactions SIII, SkM*, and SkP.
Abstract: Rotation-induced time-odd components in the nuclear mean field are analyzed using the Hartree-Fock cranking approach with effective interactions SIII, SkM*, and SkP. Identical dynamical moments ${\mathcal{J}}^{(2)}$ are obtained for pairs of superdeformed bands $^{151}\mathrm{Tb}$(2)${\mathrm{\ensuremath{-}}}^{152}$Dy(1) and $^{150}\mathrm{Gd}$(2)${\mathrm{\ensuremath{-}}}^{151}$Tb(1). The corresponding relative alignments strongly depend on which time-odd mean-field terms are taken into account in the Hartree-Fock equations.
TL;DR: In this article, a novel method of selecting \ensuremath{\gamma}-ray transitions in heavy nuclei (Ag100) at the proton drip-line has been attempted.
Abstract: A novel method of selecting \ensuremath{\gamma}-ray transitions in heavy nuclei (Ag100) at the proton drip-line has been attempted. The characteristic charged-particle radioactivity of these nuclei (alpha decay, ground-state proton decay, and \ensuremath{\beta}-delayed proton emission) has been used to tag \ensuremath{\gamma}-ray transitions recorded by the highly efficient Eurogam spectrometer. The $^{58}\mathrm{Ni}$${+}^{54}$Fe and $^{58}\mathrm{Ni}$${+}^{58}$Ni fusion-evaporation reactions, at a beam energy of 240 MeV, have been used to populate specific states of these neutron-deficient nuclei and results are presented for $^{108,109}\mathrm{Te}$, $^{109}\mathrm{I}$, and $^{113}\mathrm{Xe}$, where \ensuremath{\gamma}-ray transitions have been identified. In the case of $^{109}\mathrm{I}$, this represents the first observation of \ensuremath{\gamma}-rays from a ground-state proton emitter.
TL;DR: Results of kaon condensation are found to be qualitatively similar to previous work with chiral models, if compatibility of the kaon optical potentials is required, and generic problems with effective masses in mean field theories are discussed.
Abstract: We examine the presence of strangeness-bearing components, hyperons and kaons, in dense neutron star matter. Calculations are performed using relativistic mean field models, in which both the baryon-baryon and kaon-baryon interactions are mediated by meson exchange. Results of kaon condensation are found to be qualitatively similar to previous work with chiral models, if compatibility of the kaon optical potentials is required. The presence of strangeness, be it in the form of hyperons or kaons, implies a reduction in the maximum mass and a relatively large number of protons, sufficient to allow rapid cooling to take place. The need to improve upon the poorly known couplings of the strange particles, which determine the composition and structure of neutron stars, is stressed. We also discuss generic problems with effective masses in mean field theories.
TL;DR: The analysis of the complete fusion of nuclei on the basis of dinuclear system approach has allowed one to reveal an important feature of the fusion process of massive nuclei, that is, the appearance of the fused nucleus barrier during din nuclear system evolution to a compound nucleus.
Abstract: The evaporation residue cross sections {sigma}{sub ER} in reactions between massive nuclei have been analyzed within different models of complete fusion. The calculations in the framework of the optical model, the surface friction model, and the macroscopic dynamic model can give the results which are by few orders of magnitude different from experimental data. This takes place due to neglect of the competition between complete fusion and quasifission. A possible mechanism of compound nucleus formation in heavy-ion-induced reactions has been suggested. The analysis of the complete fusion of nuclei on the basis of dinuclear system approach has allowed one to reveal an important feature of the fusion process of massive nuclei, that is, the appearance of the fusion barrier during dinuclear system evolution to a compound nucleus. As a result, the competition between complete fusion and quasifission arises and strongly reduces the cross section of the compound nucleus formation. A model is proposed for calculation of this competition in a massive symmetric dinuclear system. This model is applied for collision energies above the Coulomb barrier. The {sigma}{sub ER} values calculated in the framework of dinuclear system approach seem to be close to the experimental data. For illustration the reactions {supmore » 100}Mo+{sup 100}Mo, {sup 110}Pd+{sup 110}Pd, and {sup 124}Sn+{sup 96}Zr have been considered.« less
TL;DR: An empirical fit is made to the world data for the proton elastic electromagnetic form factors in the range 0[lt][ital Q][sup 2][lt]10 (GeV/[ital c])[sup 2].
Abstract: We have made an empirical fit to the world data for the proton elastic electromagnetic form factors [ital G][sub [ital E][ital p]], [ital G][sub [ital M][ital p]] for 0[lt][ital Q][sup 2[lt]]30 (GeV/[ital c])[sup 2], and to the neutron electromagnetic form factors [ital G][sub [ital E][ital n]],[ital G][sub [ital M][ital n]] in the range 0[lt][ital Q][sup 2][lt]10 (GeV/[ital c])[sup 2].
TL;DR: The use of charmonium for the diagnostics of the state of hot hadronic matter produced in ultrarelativistic nucleus-nucleus collisions is discussed.
Abstract: A diagrammatic approach to quark exchange processes in meson-meson scattering is applied to the case of inelastic reactions of the type (QQ\ifmmode\bar\else\textasciimacron\fi{})+(qq\ifmmode\bar\else\textasciimacron\fi{})\ensuremath{\rightarrow}(Qq\ifmmode\bar\else\textasciimacron\fi{})+(qQ\ifmmode\bar\else\textasciimacron\fi{}), where Q and q refer to heavy and light quarks, respectively. This string-flip process is discussed as a microscopic mechanism for charmonium dissociation (absorption) in hadronic matter. The cross section for the reaction J/\ensuremath{\psi}+\ensuremath{\pi}\ensuremath{\rightarrow}D+D\ifmmode\bar\else\textasciimacron\fi{} is calculated using a potential model, which is fitted to the meson mass spectrum. The temperature dependence of the relaxation time for the J/\ensuremath{\psi} distribution in a homogeneous thermal pion gas is obtained. The use of charmonium for the diagnostics of the state of hot hadronic matter produced in ultrarelativistic nucleus-nucleus collisions is discussed.
TL;DR: Triple differential cross sections of pions in heavy ion collisions at 1 GeV/nucl are studied with the IQMD model and azimuthal correlations are investigated, finding that high $p_t$ pions are being preferentially emitted perpendicular to the event-plane.
Abstract: Triple differential cross sections of pions in heavy ion collisions at 1 GeV/nucleon are studied with the isospin quantum molecular dynamics (IQMD) model. After discussing general properties of \ensuremath{\Delta} resonance and pion production we focus on azimuthal correlations: At projectile- and target-rapidities we observe an anticorrelation in the in-plane transverse momentum between pions and protons. At c.m.-rapidity, however, we find that high ${\mathit{p}}_{\mathit{t}}$ pions are being preferentially emitted perpendicular to the event plane. We investigate the causes of those correlations and their sensitivity on the density and momentum dependence of the real and imaginary part of the nucleon and pion optical potential.
TL;DR: The calculated total Gamow-Teller strengths agree consistently with the {ital B}({ital GT}{sub +}) values deduced from ({ital n,{ital p}) data if the shell-model results are renormalized by 0.64, suggesting that this renormalization is universal.
Abstract: We study the gross properties of even-even and N=Z nuclei with A=48–64 using shell-model Monte Carlo methods. Our calculations account for all 0ħω configurations in the fp shell and employ the modified Kuo-Brown interaction KB3. We find good agreement with data for masses and total B(E2) strengths, the latter employing effective charges ep=1.35e and en=0.35e. The calculated total Gamow-Teller strengths agree consistently with the B(GT+) values deduced from (n,p) data if the shell-model results are renormalized by 0.64, as has already been established for sd-shell nuclei. The present calculations therefore suggest that this renormalization (i.e., gA=1 in the nuclear medium) is universal.
TL;DR: It is suggested that the onset of rotational motion in the rare earth nuclei is due to the promotion of the eight particle blocks to the major shells above the ones currently filling.
Abstract: Exact diagonalizations with a realistic interaction show that configurations with four neutrons in a major shell and four protons in another---or the same---major shell, behave systematically as backbending rotors. The dominance of the {ital q}{center_dot}{ital q} component of the interaction is related to an approximate ``quasi-SU3`` symmetry. It is suggested that the onset of rotational motion in the rare earth nuclei is due to the promotion of the eight particle blocks to the major shells above the ones currently filling. Assuming a ``pseudo-SU3`` coupling for the particles in the lower orbits, it is possible to account remarkably well for the observed {ital B}({ital E}2) rates at the beginning of the region.
TL;DR: A relativistic hadronic model, which incorporates nonlinear chiral symmetry and broken scale invariance, is presented and applied at the one-baryon-loop level to finite nuclei and good fits to the bulk properties of finiteuclei and single-particle spectra are obtained.
Abstract: A relativistic hadronic model for nuclear matter and finite nuclei, which incorporates nonlinear chiral symmetry and broken scale invariance, is presented and applied at the one-baryon-loop level to finite nuclei. The model contains an effective light scalar field that is responsible for the midrange nucleon-nucleon attraction and which has anomalous scaling behavior. One-loop vacuum contributions in this background scalar field at finite density are constrained by low-energy theorems that reflect the broken scale invariance of quantum chromodynamics. A mean-field energy functional for nuclear matter and nuclei is derived that contains small powers of the fields and their derivatives, and the validity of this truncation is discussed. Good fits to the bulk properties of finite nuclei and single-particle spectra are obtained.
TL;DR: It is shown that the structure change with increase of the neutron number is largely governed by the shell effect of neutron orbits, giving an important indication that clustering structure in neutron-rich B nuclei is strongly suggested by the experimental data.
Abstract: Structure of odd-even B isotopes up to the neutron dripline is studied systematically with the antisymmetrized molecular dynamics (AMD). The AMD method has already proved to be a powerful theoretical approach for the systematic study of nuclear structure in extensive region including exotic neutron-rich nuclei as well as ordinary nuclei. It is owing to its flexible nature free from any model assumptions such as the existence of clusters. The energies and other observed data of B isotopes are reproduced well. Especially very good reproduction of electromagnetic properties is obtained. The systematic behavior of the electromagnetic properties is explained in relation to the drastic change between clustering structure and shell-model-like structure. This explanation gives us an important indication that clustering structure in neutron-rich B nuclei is strongly suggested by the experimental data. It is shown that the structure change with increase of the neutron number is largely governed by the shell effect of neutron orbits. Exotic structure with new type of clustering is suggested to evolve in neutron-rich nuclei near the dripline.
TL;DR: The main aim is to develop the first steps of a transport theory which goes beyond BUU in a systematic fashion to include light cluster formation in a consistent way to include α-particle production.
Abstract: Central heavy ion collisions at E/A in the 50 to 200 MeV range can roughly be described by the initial build up of compressed and hot nuclear matter and by a sequential decompression. Some of these reactions have recently been reported [1] to end up with final fragments not heavier than α-particles, at most. This is the kind of scenario we shall address in this work. Our main aim is to develop the first steps of a transport theory which goes beyond BUU in a systematic fashion to include light cluster formation in a consistent way. By the latter we mean that cluster formation is followed throughout the entire reaction process without any ad hoc switching on and off of clustering or coalescence processes. In such a way for example memory effects in the formation process and Pauli principle will be fully accounted for. We here shall be mainly concerned with deuteron formation. However, in the end we shall shortly touch upon α-particle production as well. Our theoretical tools will be based on BCS and quasi-particle RPA theory.
TL;DR: Differences in mean particle energy components in and out of the reaction plane in semicentral collisions, depend sensitively on the relative magnitude of shock speed in normal matter and speed of sound in hot matter.
Abstract: Conditions under which compression occurs and collective expansion develops in energetic reactions of heavy nuclei, are analyzed, together with their effects on emitted light baryons and pions. Within transport simulations, it is shown that shock fronts perpendicular to beam axis form in head-on reactions. The fronts separate hot compressed matter from normal. As impact parameter increases, the angle of inclination of the fronts relative to beam axis decreases, and in-between the fronts a weak tangential discontinuity develops. Hot matter exposed to the vacuum in directions perpendicular to shock motion (and parallel to fronts), starts to expand sideways, early within reactions. Expansion in the direction of shock motion follows after the shocks propagate through nuclei, but due to the delay does not acquire same strength. Expansion affects angular distributions, mean-energy components, shapes of spectra and mean energies of different particles emitted into any one direction, and further particle yields. Both the expansion and a collective motion associated with the weak discontinuity, affect the magnitude of sideward flow within reaction plane. Differences in mean particle energy components in and out of the reaction plane in semicentral collisions, depend sensitively on the relative magnitude of shock speed in normal matter and speed of sound in hot matter.
TL;DR: In this article, isospin-mixing corrections for superallowed Fermi transitions in fp-shell nuclei are computed within the framework of the shell model, including three nuclei that are part of the set of nine accurately measured transitions as well as five cases that are expected to be measured in the future at radioactive-beam facilities.
Abstract: Isospin-mixing corrections for superallowed Fermi transitions in fp-shell nuclei are computed within the framework of the shell model. The study includes three nuclei that are part of the set of nine accurately measured transitions as well as five cases that are expected to be measured in the future at radioactive-beam facilities. We also include some new calculations for $^{10}\mathrm{C}$. With the isospin-mixing corrections applied to the nine accurately measured ft values, the conserved-vector-current hypothesis and the unitarity condition of the Cabbibo-Kobayashi-Maskawa matrix are tested.
TL;DR: The role of charm as a probe of the formation zone physics and correlations between momentum and space-time coordinates is emphasized in this paper, where the preequilibrium contribution to open charm production in nuclear collisions at =200 A GeV is calculated and shown to be sensitive to the early time evolution of the initial minijet gluon plasma.
Abstract: The preequilibrium contribution to open charm production in nuclear collisions at \ensuremath{\surd}s =200 A GeV is calculated and shown to be sensitive to the early time evolution of the initial minijet gluon plasma. The role of charm as a probe of the formation zone physics and correlations between momentum and space-time coordinates is emphasized. While ideal (Bjorken) correlation between the rapidity y and space-time rapidity \ensuremath{\eta} of minijet gluons suppresses greatly the preequilibrium yield, the minimal correlation with finite geometrical spread enhances the initial fusion rate by a factor \ensuremath{\sim}2 in the moderate ${\mathit{p}}_{\mathrm{\ensuremath{\perp}}}$\ensuremath{\sim}2--6 GeV range. That is dominated by fusion of ``semihard'' ${\mathit{p}}_{\mathrm{\ensuremath{\perp}}}$g2 GeV minijet gluons and secondary ``soft'' ${\mathit{p}}_{\mathrm{\ensuremath{\perp}}}$2 GeV gluons from initial and final state radiation. The ``intrinsic'' charm process is negligible in the midrapidity domain.
TL;DR: Open charm production during the equilibration of a gluon dominated parton plasma is calculated, with both the time-dependent temperature and parton densities given by a set of rate equations.
Abstract: Open charm production during the equilibration of a gluon dominated parton plasma is calculated, with both the time-dependent temperature and parton densities given by a set of rate equations. Including prethermal production, the total enhancement of open charm production over the initial gluon fusion depends sensitively on the initial parton density and the effective temperature. The dependence of the prethermal charm production on the space-momentum correlation in the initial parton phase-space distribution is also discussed.
TL;DR: In this article, the Compton scattering cross section on the proton has been measured at laboratory angles of 90 and 135 degrees, with tagged photons in the energy range 70-100 MeV and simultaneously using untagged photons in a range 100-148 MeV.
Abstract: The Compton scattering cross section on the proton has been measured at laboratory angles of 90{degree} and 135{degree} using tagged photons in the energy range 70--100 MeV and simultaneously using untagged photons in the range 100--148 MeV. With the aid of dispersion relations, these cross sections were used to extract the electric and magnetic polarizabilities, {bar {alpha}} and {bar {beta}} respectively, of the proton. We find {bar {alpha}}+{bar {beta}}=(15.0 {plus_minus}2.9{plus_minus}1.1{plus_minus}0.4){times}10{sup {minus}4} fm{sup 3}, in agreement with a model-independent dispersion sum rule, and {bar {alpha}} {minus}{bar {beta}} =(10.8{plus_minus}1.1{plus_minus}1.4{plus_minus}1.0){times}10{sup {minus}4} fm{sup 3}, where the errors shown are statistical, systematic, and model-dependent, respectively. A comparison with previous experiments is given and global values for the polarizabilities are extracted.
TL;DR: Using a self-consistent quark model for nuclear matter, variations of the masses of the nonstrange vector mesons, the hyperons, and the nucleon in dense nuclear matter are investigated and the changes in the hadron masses can be described in terms of the value of the scalar mean field in matter.
Abstract: Using a self-consistent quark model for nuclear matter we investigate variations of the masses of the nonstrange vector mesons, the hyperons, and the nucleon in dense nuclear matter (up to four times the normal nuclear density). We find that the changes in the hadron masses can be described in terms of the value of the scalar mean field in matter. The model is then used to calculate the density dependence of the quark condensate in-medium, which turns out to be well approximated by a linear function of the nuclear density. Some relations among the hadron properties and the in-medium quark condensate are discussed.