State In Heavy Ion Collisions Research Articles

θvacua states in heavy ion collisions in the presence of dissipation and noise

We have studied possible formation of $\Theta$ vacua states in heavy ion collisions. Random phases of the chiral fields were evolved in a finite temperature potential, incorporating the breaking of $U_A(1)$ symmetry. Initial random phases very quickly settle into oscillation around the values dictated by the potential. The simulation study indicate that an initial $\Theta$=0 state do not evolve into a $\Theta$ $\neq$ 0 state. However, an initial $\Theta$ $\neq$ 0 state, if formed in heavy ion collision, can survive, as a coherent superposition of a number of modes.

Microscopic description of Coulomb and nuclear excitation of multiphonon states in40Ca+40Cacollisions

We calculate the inelastic scattering cross sections to populate one- and two-phonon states in heavy ion collisions with both Coulomb and nuclear excitations. Starting from a microscopic approach based on random-phase approximation, we go beyond it in order to treat anharmonicities and nonlinear terms in the exciting field. These anharmonicities and nonlinearities are shown to have important effects on the cross sections both in the low energy part of the spectrum and in the energy region of the double giant quadrupole resonance. By properly introducing an optical potential, the inelastic cross section is calculated semiclassically by integrating the excitation probability over all impact parameters. A satisfactory agreement with the experimental results is obtained.

PossibleΘvacua states in heavy ion collisions

We have simulated the possible $\Theta$ vacua states in heavy ion collisions. In a quench like scenario, random phases of the chiral fields were evolved in a zero temperature potential incorporating the breaking of $U_A(1)$ symmetry. Initial random phases very quickly settles into oscillation around the values dictated by the potential. The simulation indicate that $\Theta$ vacua states that can be populated in heavy ion collisions is a coherent superposition of a number of modes.

Dibaryons with strangeness: their weak nonleptonic decay using SU(3) symmetry and how to find them in relativistic heavy-Ion collisions

Weak SU(3) symmetry is successfully applied to the weak hadronic decay amplitudes of octet hyperons. Weak nonmesonic and mesonic decays of various dibaryons with strangeness, their dominant decay modes, and lifetimes are calculated. Production estimates for the Brookhaven Relativistic Heavy Ion Collider are presented employing wave-function coalescence. Signals for detecting strange dibaryon states in heavy-ion collisions and revealing information about the unknown hyperon-hyperon interactions are outlined.

Elliptic Flow and Equation of State in Heavy Ion Collisions at SIS Energies

Elliptic Flow and Equation of State in Heavy Ion Collisions at SIS Energies

Elliptic flow and equation of state in heavy ion collisions at SIS energies

A systematic study of the elliptic flow in Au+Au collisions at energies from 0.09 to 1.49 AGeV is presented. The experimental information allows us to extract information about the reaction dynamics and, by comparison with the IQMD transport model, the Equation of State (EoS) of nuclear matter.

Flow and equation of state in heavy-ion collisions

The status of flow in heavy-ion collisions and of inference of hadronic-matter properties is reviewed.

Flow and equation of state in heavy-ion collisions

The status of flow in heavy-ion collisions and of inference of hadronic-matter properties is reviewed.

Strangeness production and propagation in relativistic heavy ion collisions at SIS energies

Strangeness production at incident energies close to the elementary production threshold is considered a tool to extract information about the properties of the hot and dense state of nuclear matter produced as a transient state in heavy ion collisions. Production yields and azimuthal anisotropies of strange particles (K +,K −,π and Φ) are measured with the FOPI detector at SIS. The distributions are examined with respect to their significance of possible in-medium modifications.

Microscopic description of Coulomb and nuclear excitation of multiphonon states in heavy ion collisions

We calculate the inelastic scattering cross sections to one- and two-phonon states in heavy ion collisions. Both Coulomb and nuclear excitations are included and their interplay is studied. Starting from a microscopic approach based on RPA, we go beyond it in order to treat anharmonicities and take explicitly into account the mixing of two-phonon states among themselves and with one-phonon states. Nonlinear terms in the exciting field are also introduced. These anharmonicities and nonlinearities are shown to have important effects on the cross sections both in the low energy part of the spectrum and in the energy region of the Double Giant Dipole Resonance.

Subthreshold kaon production and the nuclear equation of state

We reexamine in the relativistic transport model the dependence of kaon yield on the nuclear equation of state in heavy ion collisions at energies that are below the threshold for kaon production from the nucleon-nucleon interaction in free space. For Au+Au collisions at GeV/nucleon, we find that the kaon yield measured by the Kaos collaboration at GSI can be accounted for if a soft nuclear equation of state is used. We also confirm the results obtained in non-relativistic transport models that the dependence of kaon yield on the nuclear equation of state is more appreciable in heavy ion collisions at lower incident energies. We further clarify the difference between the predictions from the relativistic transport model and the non-relativistic transport model with a momentum-dependent potential.

High energy single particle states in the continuum.

This paper contains new developments of the Bonaccorso-Brink reaction model for neutron transfer to continuum states in heavy-ion collisions. The spectral distributions, escape, and spreading widths of the neutron final continuum states are calculated and studied by introducing a semiclassical S matrix describing the rescattering of the neutron on the target. By comparing to previous calculations done with an optical model S matrix we suggest a method to estimate the damping of single particle states in the continuum. Our calculations for the transfer cross sections and for the single particle widths are compared to available experimental data. The results of the comparison support the interpretation of the structures in the experimental spectra up to an excitation energy as high as ${\mathit{E}}_{\mathit{x}}$\ensuremath{\sim}20 MeV in $^{208}\mathrm{Pb}$ and ${\mathit{E}}_{\mathit{x}}$\ensuremath{\sim}30 MeV in $^{91}\mathrm{Zr}$ as due to the population of single particle states of high spin.

A FULL-ACCEPTANCE DETECTOR FOR SSC PHYSICS AT LOW AND INTERMEDIATE MASS SCALES: AN EXPRESSION OF INTEREST TO THE SSC

A FULL-ACCEPTANCE DETECTOR FOR SSC PHYSICS AT LOW AND INTERMEDIATE MASS SCALES: AN EXPRESSION OF INTEREST TO THE SSC

Cluster-cluster collisions. II. Cluster molecules — a stable state of matter?

Electronic and atomic structure as well as the energetic stabililty of “cluster molecules” found in cluster fusion reactions are investigated. The Na 9Na 9 cluster molecule formed in collisions of two Na 9 clusters has a binding energy which is very close to that of the nearly spherical “magic” Na 18 cluster and might be regarded as a stable state of atomic matter. Also in the initially “doublemagic” system Na 8 + Na 8 a molecular cluster configuration is found. However, in contrast to the former one, Na 8Na 8 is unstable; its appearance very much resembles “nuclear molecules” which show up as transition state in heavy-ion collisions.

Effective interactions and the equation of state in heavy ion collisions

We point out that the effective fields in a heavy ion collision are not only momentum dependent, as e.g. the optical model, but also momentum space configuratio n dependent, leading to a double self consistency. The momentum configurations vary strongly in the evolution of a heavy ion collision and are very different from those of the ground state of nuclear matter. We discuss, this dependence in field theoretical models for thermalized and interpenetrating nuclear matter. We estimate the repulsive effects on the equation of state in these limiting cases and for heavy ion collisions. It is found that the effective equation of state in a heavy ion collision acquires considerable stiffness. We discuss ways to include this effect in realistic calculations of heavy ion collisions.

Two-centre shell model description of quasi-molecular resonance states in heavy-ion collisions

The structural configurations of the quasi-molecular resonance states, at energies both below and above the Coulomb barrier, are studied within the orbiting cluster model approach. A generalized moment of inetia expression for the two-centre shell-model nuclear shape, that applies also to dinuclear configurations, is used. Applications of the method are made to 12C + 12C, 16O + 12C, 16O + 16O, 24Mg + 24Mg and 28Si + 28Si systems. Further experimental investigations are needed.

Generalised non-equilibrium equation of state for nuclear matter with momentum-dependent interactions

A generalisation of the equation of state (EOS) for nuclear matter to non-equilibrium situations is presented using momentum-dependent interactions. This concept is important for the case of two interpenetrating nuclei in the early state of heavy-ion collisions. The streaming-through of the two nuclei enters directly into the generalised non-equilibrium EOS via an additional Lagrange multiplier in the grand partition function. The importance of this concept is demonstrated for momentum-dependent interactions (Skyrme forces and a relativistic meson field theory) in the independent-particle approximation.

Neutron decay of excited nuclear states in heavy ion collisions.

The neutron decay of excited states of $^{7}\mathrm{Li}$ and $^{8}\mathrm{Li}$ has been investigated in the $^{14}\mathrm{Ag}$ reaction at E/A=35 MeV. Specifically, the production of the 2.255 MeV unbound state in $^{8}\mathrm{Li}$ and the 7.456 MeV unbound state in $^{7}\mathrm{Li}$ have been measured. Comparison of the production of those two states to that of previously measured lower-lying excited states indicates a nuclear temperature of 3.0(4) MeV. The fraction of the $^{7}\mathrm{Li}$ and $^{6}\mathrm{Li}$ nuclei from the neutron decay of these states is 6(2)% and 4(1)%, respectively, which is significant in that it can resolve some of the discrepancies between recent nuclear temperature measurements.

Excitation of discrete particle-unbound states in heavy-ion collisions

Abstract Neutron spectra in coincidence with fragments have been observed in 14 N- 165 Ho collisions at 490 MeV. Contributions to the spectra from excited light fragments are very pronounced when the fragments detector and the neutron detector are in colinear geomwtry. Relative velocity spectra then reveal that neutron decay of a single, well-known excited state dominates. In inclusive spectra of neutrons or protons these effects are still present and may not be disregarded.

Temperatures in heavy-ion collisions from pion multiplicities

A thermodynamically consistent treatment of the nuclear interaction is employed to study the dependence of pion production on the nuclear equation of state in heavy-ion collisions. Massive baryon resonances, heavy mesons and the Bose condensation of pions are incorporated into a macrocanonical relativistic quantum-statistical treatment of the highly excited system. The measured pion multiplicities, which vary over eight orders of magnitude in the bombarding energy range from 30 MeV/nucleon to 4 GeV/nucleon, are reproduced within a simple one-dimensional fluiddynamical model if it is assumed that nuclear matter is rather incompressible. The pion yields are in this model directly related to the compression energy, which amounts to one-half of the total center-of-mass energy at all BEVALAC energies. The maximum compression derived is uncertain by about 10% and 30% at E lab = 0.4 and 1.8 GeV/ nucleon, respectively. The temperatures of the system in the moment of the chemical freeze-out of the pion/delta degree of freedom are determined from the measured pion yields and range from 10 MeV to 100 MeV. An extrapolation to CERN/BNL energies, i.e. E lab > 10 GeV/ nucleon, yields T = 150–200 MeV. A strong energy dependence of the cross sections and the slopes of hard γ's is predicted by this model. The calculated photon yields are in surprising agreement with the data on γ- production at intermediate energies.