arXiv subjects
Publications and source records attributed to P. Danielewicz.
Source images are extracted from two-particle correlations constructed from strange and non-strange hadrons produced in 6 AGeV Au + Au collisions. Very different source images result from pp vs p$Λ$ vs $π^-π^-$ correlations. These observations suggest important differences in the space-time emission histories for protons, pions and neutral strange baryons produced in the same events.
Isoscaling is found to hold for fragment yields in the antisymmetrized molecular dynamics (AMD) simulations for collisions of calcium isotopes at 35 MeV/nucleon. This suggests the applicability of statistical considerations to the dynamical fragment emission. The observed linear relationship between the isoscaling parameters and the isospin asymmetry of fragments supports the above suggestion. The slope of this linear function yields information about the symmetry energy in low density region where multifragmentation occurs.
We discuss the accuracy of mass models for extrapolating to very asymmetric nuclei and the impact of such extrapolations on the predictions of isotopic observables in multifragmentation. We obtain improved mass predictions by incorporating measured masses and extrapolating to unmeasured masses with a mass formula that includes surface symmetry and Coulomb terms. We find that using accurate masses has a significant impact on the predicted isotopic observables.
Imaging technique is applied to two-proton correlation functions to extract quantitative information about the space-time properties of the emitting source and about the fraction of protons that can be attributed to fast emission mechanisms. These new analysis techniques resolve important ambiguities that bedeviled prior comparisons between measured correlation functions and those calculated by transport theory. Quantitative comparisons to transport theory are presented here. The results of the present analysis differ from those reported previously for the same reaction systems. The shape of the two-proton emitting sources are strongly sensitive to the details about the in-medium nucleon-nucleon cross sections and their density dependence.
Nuclear collisions can compress nuclear matter to densities achieved within neutron stars and within core-collapse supernovae. These dense states of matter exist momentarily before expanding. We analyzed the flow of matter to extract pressures in excess of 10^34 pascals, the highest recorded under laboratory-controlled conditions. Using these analyses, we rule out strongly repulsive nuclear equations of state from relativistic mean field theory and weakly repulsive equations of state with phase transitions at densities less than three times that of stable nuclei, but not equations of state softened at higher densities because of a transformation to quark matter.
The breakup of the radioactive 17F nucleus into a proton and 16O is studied for the reaction 17F + 208Pb --> p + 16O + 208Pb at 65 MeV/nucleon. The possibility of using this reaction as a test case for studying dynamical Coulomb reacceleration effects is assessed. It is shown that the reaction is dominated by elastic nuclear breakup (diffraction dissociation).
Extraction of bulk nuclear properties by comparing reaction observables to results from semiclassical transport-model simulations is discussed. Specific properties include the nuclear viscosity, incompressibility and constraints on the nuclear pressure at supranormal densities.
Hadronic transport models may be utilized to extract bulk nuclear properties. Deduction of in-medium nucleon-nucleon cross sections and of nuclear viscosity is discussed, as well as the extraction of momentum dependence of nucleonic mean field. Moreover, determination of the nuclear incompressibility and of constraints on the nuclear pressure at supranormal densities is described.
We investigate two-proton correlation functions for reactions in which fast dynamical and slow evaporative proton emission are both present. In such cases, the width of the correlation peak provides the most reliable information about the source size of the fast dynamical component. The maximum of the correlation function is sensitive to the relative yields from the slow and fast emission components. Numerically inverting the correlation function allows one to accurately disentangle fast dynamical from slow evaporative emission and extract details of the shape of the two-proton source.
Proton elliptic flow is studied as a function of impact-parameter $b$, for two transverse momentum cuts in 2 - 6 AGeV Au + Au collisions. The elliptic flow shows an essentially linear dependence on b (for $1.5 < b < 8$ fm) with a negative slope at 2 AGeV, a positive slope at 6 AGeV and a near zero slope at 4 AGeV. These dependencies serve as an important constraint for discriminating between various equations of state (EOS) for high density nuclear matter, and they provide important insights on the interplay between collision geometry and the expansion dynamics. Extensive comparisons of the measured and calculated differential flows provide further evidence for a softening of the EOS between 2 and 6 GeV/nucleon.
Nuclear equation of state plays an important role in the evolution of the Universe, in supernova explosions and, thus, in the production of heavy elements, and in stability of neutron stars. The equation constrains the two- and three-nucleon interactions and the quantum chromodynamics in nonperturbative regime. Despite the importance of the equation, though, its features had remained fairly obscure. The talk reviews new results on the equation of state from measurements of giant nuclear oscillations and from studies of particle emission in central collisions of heavy nuclei.
The interplay between spectator and participant matter in heavy-ion collisions is investigated in the context of a microscopic transport model. Transport simulations show that flow patterns for the participant matter are strongly influenced by the presence of the nearby spectator matter. However, the influence is mutual. During the explosion of the participant zone, the spectator matter acquires a transverse momentum $ $ that shows sensitivity to the nuclear incompressibility and to the momentum dependence of the nuclear mean field (MF). An observed change in the net average momentum per nucleon, $Δ|< {\bf P}/A >|$, can be associated with the momentum dependence of the MF. For a momentum-dependent MF and a low impact parameter in a heavy system, the spectators may emerge faster than in the initial state, accelerated by the violent participant explosion. The average excitation energy and the mass of the spectators, in contrast to the momentum, show little sensitivity to the nuclear equation of state.
We examine the possibility of extracting non-Gaussian sources from two-particle correlations in heavy-ion reactions. Non-Gaussian sources have been predicted in a variety of model calculations and may have been seen in various like-meson pair correlations. As a tool for this investigation, we have developed an improved imaging method that relies on a Basis spline expansion of the source functions with an improved implementation of constraints. We examine under what conditions this improved method can distinguish between Gaussian and non-Gaussian sources. Finally, we investigate pion, kaon, and proton sources from the p-Pb reaction at 450 GeV/nucleon and from the S-Pb reaction at 200 GeV/nucleon studied by the NA44 experiment. Both the pion and kaon sources from the S-Pb correlations seem to exhibit a Gaussian core with an extended, non-Gaussian halo. We also find evidence for a scaling of the source widths with particle mass in the sources from the p-Pb reaction.
Within the pure Coulomb breakup mechanism, we investigate the one-neutron removal reaction of the type A(a,b$γ$)X with $^{11}$Be and $^{19}$C projectiles on a heavy target nucleus $^{208}$Pb at the beam energy of 60 MeV/nucleon. Our intention is to examine the prospective of using these reactions to study the structure of neutron rich nuclei. Integrated partial cross sections and momentum distributions for the ground as well as excited bound states of core nuclei are calculated within the finite range distorted wave Born approximation as well as within the adiabatic model of the Coulomb breakup. Our results are compared with those obtained in the studies of the reactions on a light target where the breakup proceeds via the pure nuclear mechanism. We find that the transitions to excited states of the core are quite weak in the Coulomb dominated process as compared to the pure nuclear breakup.
The status of flow in heavy-ion collisions and of inference of hadronic-matter properties is reviewed.
Within a microscopic statistical description of heavy ion collisions, we investigate the effect of the medium on the formation of light clusters. The dominant medium effects are self-energy corrections and Pauli blocking that produce the Mott effect for composite particles and enhanced reaction rates in the collision integrals. Microscopic description of composites in the medium follows the Dyson equation approach combined with the cluster mean-field expansion. The resulting effective few-body problem is solved within a properly modified Alt-Grassberger-Sandhas formalism. The results are incorporated in a Boltzmann-Uehling-Uhlenbeck simulation for heavy ion collisions. The number and spectra of light charged particles emerging from a heavy ion collision changes in a significant manner in effect of the medium modification of production and absorption processes.
Nuclear matter within the liquid-gas phase transition region is investigated in a mean-field two-component Fermi-gas model. Following largely analytic considerations, it is shown that: (1) Due to density dependence of asymmetry energy, some of the neutron excess from the high-density phase could be expelled into the low-density region. (2) Formation of clusters in the gas phase tends to counteract this trend, making the gas phase more liquid-like and reducing the asymmetry in the gas phase. Flow of asymmetry between the spectator and midrapidity region in reactions is discussed and a possible inversion of the flow direction is indicated.
Midrapidity nucleon elliptic flow is studied within the Boltzmann-equation simulations of symmetric heavy-ion collisions. The simulations follow a lattice Hamiltonian extended to relativistic transport. It is demonstrated that in the peripheral heavy-ion collisions the high-momentum elliptic flow is strongly sensitive to the momentum dependence of mean field at supranormal densities. The high transverse-momentum particles are directly and exclusively emitted from the high-density zone in the collisions, while remaining particles primarily continue along the beam axis. The elliptic flow was measured by the KaoS Collaboration as a function of the transverse momentum at a number of impact parameters in Bi + Bi collisions at 400, 700, and 1000 MeV/nucleon. The observed elliptic anisotropies in peripheral collisions, which quickly rise with momentum, can only be explained in simulations when assuming a strong momentum dependence of nucleonic mean field. This momentum dependence must strengthen with the rise of density above normal. The mean-field parametrizations, which describe the data in simulations with various success, are confronted with mean fields from microscopic nuclear-matter calculations. Two of the microscopic potentials in the comparisons have unacceptably weak momentum-dependencies at supranormal densities. The optical potentials from the Dirac-Brueckner-Hartree-Fock calculations, on the other hand, together with the UV14 + TNI potential from variational calculations, agree rather well within the region of sensitivity with the parametrized potentials that best describe the data.