Showing papers on "Nuclear matter published in 1992"
TL;DR: It is pointed out that the general results pertain to relativistic nuclear collisions in the so-called stopping or baryon-rich domain where there are three conserved charges (baryon, electric, and strangeness), and impact the expected phase transition from confined hadronic matter to quark matter as regards signals that are supposedly driven by pressure.
Abstract: We consider how first-order phase transitions in systems having more than one conserved charge (multicomponent systems) differ from those in systems having only one. In general, the properties of the transition are quite different in the two cases. Perhaps most importantly the pressure varies continuously with the proportion of phases in equilibrium, and is not a constant in the mixed phase as in the example of the gas-liquid transition in familiar one-component systems. We identify the microphysics responsible for the difference. In the case that one of the conserved charges is the electric charge, a geometrical structure in the mixed phase is expected. As an example, possible consequences are developed for the structure of a neutron star in which the transition to quark matter in the core occurs. It is also pointed out that the general results pertain to relativistic nuclear collisions in the so-called stopping or baryon-rich domain where there are three conserved charges (baryon, electric, and strangeness), and impact the expected phase transition from confined hadronic matter to quark matter as regards signals that are supposedly driven by pressure. The physics discussed here is also relevant to the subunclear gas-liquid transition that is under study in lower-energy nuclear collisions.
603 citations
TL;DR: The trace anomaly and the Hellmann-Feynman theorem lead to a prediction of the gluon condensate that is model independent to first order in the nucleon density, and this prediction implies that the quark condensates is reduced considerably at nuclear matter saturation density.
Abstract: Quark and gluon condensates in nuclear matter are studied. These in-medium condensates may be linked to a wide range of nuclear phenomena and are important inputs to QCD sum-rule calculations at finite density. The Hellmann-Feynman theorem yields a prediction of the quark condensate that is model independent to first order in the nucleon density. This linear density dependence, with slope determined by the nucleon \ensuremath{\sigma} term, implies that the quark condensate is reduced considerably at nuclear matter saturation density---it is roughly 25--50 % smaller than the vacuum value. The trace anomaly and the Hellmann-Feynman theorem lead to a prediction of the gluon condensate that is model independent to first order in the nucleon density. At nuclear matter saturation density, the gluon condensate is about 5% smaller than the vacuum value. Contributions to the in-medium quark condensate that are of higher order in the nucleon density are estimated with mean-field quark-matter calculations using the Nambu--Jona-Lasinio and Gell-Mann--L\'evy models. Treatments of nuclear matter based on hadronic degrees of freedom are also considered, and the uncertainties are discussed.
246 citations
TL;DR: A relativistic density-dependent Hartree approach for finite nuclei, where the coupling constants of the relativism Hartree Lagrangian are made density dependent and are obtained from the relativist Brueckner-Hartree-Fock results of nuclear matter.
Abstract: We develop a relativistic density-dependent Hartree approach for finite nuclei, where the coupling constants of the relativistic Hartree Lagrangian are made density dependent and are obtained from the relativistic Brueckner-Hartree-Fock results of nuclear matter. The calculated results on binding energies and root mean square radii of {sup 16}O and {sup 40}Ca agree very well with experiment. The charge densities from electron scattering are also calculated and their dependence on the nucleon-nucleon interaction is discussed in relation with nuclear matter properties.
166 citations
TL;DR: The model consists of Skyrme-type interactions in four-, six-, and eight-fermion point couplings in a manifestly nonrenormalizable Lagrangian, which also contains derivative terms to simulate the finite ranges of the mesonic interactions.
Abstract: We present initial results in the calculation of nuclear ground state properties in a relativistic Hartree approximation. Our model consists of Skyrme-type interactions in four-, six-, and eight-fermion point couplings in a manifestly nonrenormalizable Lagrangian, which also contains derivative terms to simulate the finite ranges of the mesonic interactions. A self-consistent procedure has been developed to solve the model equations for several nuclei simultaneously by use of a generalized nonlinear least-squares adjustment algorithm. With this procedure we determine the nine coupling constants of our model so as to reproduce measured ground state binding energies, rms charge radii, and spin-orbit splittings of selected closed major shell and closed subshell nuclei in nondeformed regions. The coupling constants obtained in this way predict these same observables for a much larger set of closed shell spherical nuclei to good accuracy and also predict these quantities for similar nuclei far outside the valley of beta stability. Finally, they yield properties of saturated nuclear matter in agreement with recent relativistic mean meson field approaches.
154 citations
TL;DR: In this article, the binding energy of quarkonium with nuclei in the m Q → ∞ limit of QCD was studied, where the dominant contribution to the interaction is from two-gluon operators.
123 citations
TL;DR: When one is looking at the area of normal nuclei one knows for a very long time that there exists a valley of stability and that the binding energy can be well described by the Bethe-Weizsacker formula, so one has to deal with a three dimensional space of nuclear composites of nucleons and hyperons.
Abstract: When one is looking at the area of normal nuclei one knows for a very long time that there exists a valley of stability and that the binding energy can be well described by the Bethe-Weizsacker formula. Nowadays, it is assumed that QCD is the underlying basic theory. If one studies another degree of freedom of QCD, the strangeness, one realizes that this opens a new dimension of finite nuclear systems. Hence, one has to deal with a three dimensional space of nuclear composites of nucleons and hyperons.
121 citations
TL;DR: In this paper, the evolution of the hot central region produced in central heavy ion collisions is analyzed and the main properties of the final state can be understood as a result of an adiabatic expansion process.
115 citations
TL;DR: A simple relation between the nucleon-nucleon scattering cross sections in vacuum and in nuclear matter is proposed, which consistently takes into account the velocity dependence of the nuclear mean field and Pauli blocking, and is shown to be fairly accurate.
Abstract: A simple relation between the nucleon-nucleon scattering cross sections in vacuum and in nuclear matter is proposed It consistently takes into account the velocity dependence of the nuclear mean field and Pauli blocking, and is shown to be fairly accurate It is used to study the mean free path of nucleons in nuclear matter and the imaginary part of the optical potential It is also used with the local density approximation and the correlated Glauber approximation to calculate the transparency of nuclei as measured by (e,e'p) reactions The Pauli blocking, velocity dependence of the nuclear mean field, and the ground-state correlations increase the transparency, and all the three effects are necessary to explain the observed transparencies of $^{12}\mathrm{C}$, $^{27}\mathrm{Al}$, $^{58}\mathrm{Ni}$, and $^{181}\mathrm{Ta}$ for recoiling 180 MeV protons
113 citations
TL;DR: Properties of neutron stars derived from the hybrid derivative coupling model of nuclear field theory are studied, with limits on rotation imposed by gravitation-radiation-reaction instabilities as moderated by viscosity.
Abstract: Properties of neutron stars derived from the hybrid derivative coupling model of nuclear field theory are studied. Generalized beta equilibrium with all baryon types to convergence is allowed. Hyperon couplings compatible with the inferred binding energy of the lambda hyperon in saturated nuclear matter predict a large hyperon population, with neutrons having a bare majority population in a 1.5{ital M}{sub {circle dot}} neutron star. Among the properties studied are the limits on rotation imposed by gravitation-radiation-reaction instabilities as moderated by viscosity. These instabilities place a lower limit on rotational periods of neutron and hybrid stars of about 1 ms.
86 citations
TL;DR: Within the framework of the Dirac-Brueckner (DB) approach, the properties of dense nuclear and neutron matter are investigated using realistic nucleon-nucleon ({ital NN}) interactions which are derived from relativistic meson-field theory and describe the two-n nucleon system quantitatively.
Abstract: Within the framework of the Dirac-Brueckner (DB) approach, the properties of dense nuclear and neutron matter are investigated using realistic nucleon-nucleon (NN) interactions which are derived from relativistic meson-field theory and describe the two-nucleon system quantitatively. Single-particle potentials, equations of state, nucleon effective masses, Landau parameters, and speeds of sound are calculated and analyzed as functions of density, for both nuclear and neutron matter. In the DB approach, the equation of state comes out stiffer than in the most sophisticated nonrelativistic calculation, but softer than in the Walecka model. Possible extensions of the present approach to nucleon-nucleus scattering and nucleus-nucleus collisions are also discussed.
83 citations
TL;DR: In this article, the influence of the density and momentum dependence of the interaction on the time evolution of heavy-ion collisions is studied in detail, and it is shown that the momentum dependence strongly affects the nuclear density and temperature of the nuclear matter formed during collisions.
TL;DR: The self-energies of quasinucleon states in nuclear matter are studied using QCD sum-rule methods and are found to be comparable to those suggested by relativistic nuclear physics phenomenology.
Abstract: The self-energies of quasinucleon states in nuclear matter are investigated using a finite-density QCD sum-rule approach developed previously. The sum rules are obtained for a general QCD interpolating field for the nucleon. The key phenomenological inputs are the nucleon \ensuremath{\sigma} term, the strangeness content of the nucleon, and quark and gluon distribution functions deduced from deep-inelastic scattering. The emphasis is on testing the sensitivity and stability of sum-rule predictions to variations of the condensates and other input parameters. At nuclear matter saturation density, the Lorentz vector self-energy is found to be positive with a magnitude of a few hundred MeV, which is comparable to that suggested by relativistic nuclear phenomenology. This result is quite stable. The prediction for the scalar self-energy is very sensitive to the undertermined values of the in-medium four-quark condensates.
TL;DR: In this paper, a dependence of the inclusive p T spectra in p + A provides novel constraints on gluon shadowing in nuclei, and it is shown that the dependence on the pT spectra provides new information on the energy loss mechanisms in dense matter near the quark-gluon plasma transition.
TL;DR: In this paper, the self-consistent random phase approximation (RPA) response function of infinite Fermi systems is derived from an effective interaction with velocity and density dependence, or equivalently from a local energy density functional.
TL;DR: Direct URCA processes, occurring in neutron-star matter with a proton fraction exceeding the critical value of (11--15)%, can strongly enhance the bulk viscosity of the matter.
Abstract: Direct URCA processes, occurring in neutron-star matter with a proton fraction exceeding the critical value of (11-15)%, can strongly enhance the bulk viscosity of the matter.
TL;DR: The spectral function of a rho meson that is at rest in dense hadronic matter and couples strongly to the pion is studied in the vector dominance model by including the effect of the delta-hole polarization of the pions.
Abstract: The spectral function of a rho meson that is at rest in dense hadronic matter and couples strongly to the pion is studied in the vector dominance model by including the effect of the delta-hole polarization of the pion. With the free rho-meson mass in the Lagrangian, we find that both the rho-meson peak and width increase with increasing nuclear density, and that a low-mass peak appears at invariant mass around three times the pion mass. Including the decreasing density-dependent hadron masses in the Lagrangian as suggested by the scaling law of Brown and Rho, we find instead that the rho peak moves to smaller invariant masses with diminishing strength when the nuclear density increases. The low-mass peak also shifts down with increasing density and becomes more pronounced. The relevance of the rho-meson property in dense matter to delepton production in heavy-ion collisions is discussed.
TL;DR: In this paper, a microscopic calculation of the one-body Green function for a realistic model of nuclear matter, including spin and tensor correlations, is presented, based on the theory of orthogonal correlated basis functions, taking into account up to two-particle (hole) one-hole (particle) correlated bsiss-function states in the particle spectral function.
TL;DR: In this article, the Dirac-Brueckner-Hartree-Fock calculations of nuclear matter are parametrized by the relativistic σω mean-field theory with scalar and vector nonlinear self-interactions.
TL;DR: The nucleon self-energy is evaluated in a model that has proper analytical properties, satisfies the low density theorem and provides values of Im {Sigma} for high densities comparable to those of realistic microscopic approaches.
Abstract: We have evaluated the nucleon self-energy in a model that has proper analytical properties, satisfies the low density theorem and provides values of Im \ensuremath{\Sigma} for high densities comparable to those of realistic microscopic approaches. The model, however, relies only upon the NN experimental cross sections and the empirical spin-isospin interaction, which induces an important polarization of the medium. The results obtained for the spectral functions, occupation numbers, and effective masses are quite reasonable. The model does not give the absolute value of the nucleon self-energy but only differences with respect to the Fermi energy. On the other hand, it provides an easy and efficient way of evaluating many of the nucleon properties in the nuclear medium.
TL;DR: A theoretical analysis of collective momentum transfer is performed in heavy-ion reactions below 100 MeV/nucleon in the Landau-Vlasov approach and the question whether the flow provides information on out-of-equilibrium matter properties is investigated.
Abstract: A theoretical analysis of collective momentum transfer is performed in heavy-ion reactions below 100 MeV/nucleon in the Landau-Vlasov approach. The nucleon-nucleon cross section, atomic mass, compressibility, and effective mass dependences are analyzed. The simulation of detector acceptances and of finite number of detected particles are discussed. In connection with recent experiments, theoretical results and experimental data are confronted taking into account the experimental constraints. Finite range forces of the Gogny type connected with different nuclear matter incompressibilities are used and the ensuing sensitivity of the flow is studied. The question whether the flow provides information on out-of-equilibrium matter properties is investigated.
TL;DR: In this article, the absorption cross sections from photon, hadron, and nucleus-nucleus collisions are plotted against the length of the final state trajectory in nuclear matter and the equality of cross sections implies that additional suppression effects from a quark-gluon plasma are not visible.
Abstract: The data ofJ/ψ-production cross sections from photon, hadron and nucleus-nucleus collisions are plotted against the length of thec
$$\bar c$$
final state trajectory in nuclear matter. A value for the absorption cross section per nucleon of σ
abs
ψN
=(6.2±0.3) mb is deduced from the baryon and photon induced reactions and σ
abs
ψN
=(6.9±1.0) mb from the nucleus-nucles collisions. The equality of cross sections implies that additional suppression effects from a quark-gluon plasma are not visible.
TL;DR: In this paper, two new versions of hyperon-nucleon interaction models (A and B) are presented, in which the explicit energy dependence of the original models A and B is removed in order to simplify application in nuclear structure calculations.
Abstract: Hyperon-nucleon interaction models (A, B), which have been developed in the meson-exchange framework by the Julich group, are reviewed, with some emphasis on characteristic conceptual differences compared to corresponding interactions constructed by the Nijmegen group. We report on two new versionsA and\(\tilde B\) in which the explicit energydependence of the original models A and B is removed in order to simplify application in nuclear structure calculations. As a byproduct of our analysis we find that the resulting SU(3)-parameters likeF/(F+D) ratios do depend on the specific model used an on approximations applied. While all models provide a reasonable description of the scarce cross-section data, sizeable differences occur in the, so far unmeasured, spin observables, especially between our models and the Nijmegen soft-core model NSC. This demonstrates clearly that a measurement of such observables can easily discriminate between present models and thus shed some light on various aspects of the hyperon-nucleon interactions like e.g. the proper choice of parameter constraints. In addition, the results obtained with the energy-independent potentials (A,\(\tilde B\)) in a conventional first-order Brueckner calculation for a λ-hyperon in nuclear matter are presented. The binding energy BΛ(∞) of a λ-hyperon in nuclear matter was found to be 29.8 MeV (32.0 MeV) for model A(\(\tilde B\).
CERN1
TL;DR: In this paper, a modification of the structure functions in nuclei leads to reduced production relative to pp interactions, and parton scattering in nuclear matter broadens the transverse momentum spectrum.
TL;DR: In this article, the structure function ratio of infinite nuclei to the deuteron has been extrapolated to infinite nuclear matter using the local density approximation, which is more amenable to quantitative theoretical interpretation.
TL;DR: In this article, the Brueckner G-matrix has been used to calculate the effective nucleon-nucleon potential and the nucleon nucleon cross sections in a medium from the basic Reid soft core potential.
TL;DR: In this article, the theoretical aspects of condensation in neutron matter are considered on the basis of SU(3) L ×SU( 3) R current algebra and PCAC and it is clarified that the critical condition is different from charged pion condensation and the weak interaction plays a significant role near the threshold.
TL;DR: The phase transition to a quark-gluon plasma, described by a bag-model equation of state, is studied in an approximation suitable for infinite nuclear matter.
Abstract: The nuclear-matter equation of state is studied with a momentum-dependent effective interaction. The incompressibility and the zero-temperature optical potential are calculated analytically. The momentum distribution of nucleons is examined and the effect of the momentum dependence on pion-production rates is illustrated. The phase transition to a quark-gluon plasma, described by a bag-model equation of state, is studied in an approximation suitable for infinite nuclear matter.
TL;DR: Bounds suggest that a prompt conversion could be achieved inside the Kelvin-Helmholtz cooling era of a compact star life but not much after it, giving support to earlier expectations for nonstandard type-II supernova scenarios.
Abstract: We investigate the nucleation of strange quark matter inside hot, dense nuclear matter. Applying Zel'dovich's kinetic theory of nucleation we find a lower limit of the temperature {ital T} for strange-matter bubbles to appear, which happens to be satisfied inside the Kelvin-Helmholtz cooling era of a compact star life but not much after it. Our bounds thus suggest that a prompt conversion could be achieved, giving support to earlier expectations for nonstandard type-II supernova scenarios.
TL;DR: In this paper, a large energy gap is found if one adopts the bare nucleon-nucleon interaction in the gap equation, and the relevance of the results for the structure of neutron stars, nuclear matter saturation and superfluidity in finite nuclei is briefly discussed.
TL;DR: This work obtains a semiquantitative description of the data (the so-called European Muon Collaboration effect) and shows that the conventional treatment based on nucleon binding is quantitatively unreliable.
Abstract: It has recently been shown that the twist-two valence quark distributions calculated in the MIT bag model are in reasonable agreement with world data. Furthermore, several authors have constructed mean-field theories which reproduce the saturation properties of nuclear matter in terms of a mean-field theory of nonoverlapping bags, self-consistently bound by scalar and vector meson exchange. By using a local density approximation we combine these developments to microscopically investigate the structure functions of finite nuclei. Not only do we obtain a semiquantitative description of the data (the so-called European Muon Collaboration effect) but we also show that the conventional treatment based on nucleon binding is quantitatively unreliable.