Fragments in Gaussian Wave-Packet Dynamics with and without correlations

Generalization of Gaussian trial wave functions in quantum molecular dynamics models is introduced, which allows for long-range correlations characteristic for composite nuclear fragments. We demonstrate a significant improvement in the description of light fragments with correlations. Utilizing either type of Gaussian wave functions, with or without correlations, however, we find that we cannot describe fragment formation in a dynamic situation. Composite fragments are only produced in simulations if they are present as clusters in the substructure of original nuclei. The difficulty is traced to the delocalization of wave functions during emission. Composite fragments are produced abundantly in the Gaussian molecular dynamics in the limit $\hbar \rightarrow 0$.Comment: 22 pages, revtex, 6 postscript figure

Towards the 3D-Imaging of Sources

Geometric details of a nuclear reaction zone, at the time of particle emission, can be restored from low relative-velocity particle-correlations, following imaging. Some of the source details get erased and are a potential cause of problems in the imaging, in the form of instabilities. These can be coped with by following the method of discretized optimization for the restored sources. So far it has been possible to produce 1-dimensional emission source images, corresponding to the reactions averaged over all possible spatial directions. Currently, efforts are in progress to restore angular details.Comment: Talk given at the Int. Workshop on Hot and Dense Matter in Relativistic Heavy Ion Collisions, March 24-27, 2004, Budapest; 10 pages, 6 figure

From fusion to total disassembly: global stopping in heavy-ion collisions

Using the quantum molecular dynamics model, we aim to investigate the emis- sion of light complex particles, and degree of stopping reached in heavy-ion colli- sions. We took incident energies between 50 and 1000 MeV/nucleon. In addition, central and peripheral collisions and different masses are also considered. We ob- serve that the light complex particles act in almost similar manner as anisotropic ratio. In other words, multiplicity of light complex particles is an indicator of global stopping in heavy-ion collisions. We see that maximum light complex particles and stopping is obtained for heavier masses in central collisions

Heavy Ion Dynamics and Neutron Stars

Some considerations are reported, freely inspired from the presentations and discussions during the Beijing Normal University Workshop on the above Subject, held in July 2007. Of course this cannot be a complete summary but just a collection of personal thougths aroused during the meeting.Comment: 11 pages, no figures, Summary Talk, Int.Workshop on "Nuclear Dynamics in Heavy Ion Collisions and Neutron Stars", Beijing Normal Univ. July 07, to appear in Int.Journ.Modern Physics E (2008

Optimized Discretization of Sources Imaged in Heavy-Ion Reactions

We develop the new method of optimized discretization for imaging the relative source from two particle correlation functions. In this method, the source resolution depends on the relative particle separation and is adjusted to available data and their errors. We test the method by restoring assumed pp sources and then apply the method to pp and IMF data. In reactions below 100 MeV/nucleon, significant portions of the sources extend to large distances (r > 20 fm). The results from the imaging show the inadequacy of common Gaussian source-parametrizations. We establish a simple relation between the height of the pp correlation function and the source value at short distances, and between the height and the proton freeze-out phase-space density.Comment: 36 pages (inc. 9 figures), RevTeX, uses epsf.sty. Submitted to Phys. Rev.

Disappearance of Elliptic Flow: A New Probe for the Nuclear Equation of State

Using a relativistic hadron transport model, we investigate the utility of the elliptic flow excitation function as a probe for the stiffness of nuclear matter and for the onset of a possible quark-gluon-plasma (QGP) phase-transition at AGS energies 1 < E_Beam < 11 AGeV. The excitation function shows a strong dependence on the nuclear equation of state, and exhibits characteristic signatures which could signal the onset of a phase transition to the QGP.Comment: 11 pages, 4 Postscript figures, uses epsf.sty, submitted to Physical Review Letter

The Influence of in-medium NN cross-sections, symmetry potential and impact parameter on the isospin observables

We explore the influence of in-medium nucleon-nucleon cross section, symmetry potential and impact parameter on isospin sensitive observables in intermediate-energy heavy-ion collisions with the ImQMD05 code, a modified version of Quantum Molecular Dynamics model. At incident velocities above the Fermi velocity, we find that the density dependence of symmetry potential plays a more important role on the double neutron to proton ratio $DR(n/p)$ and the isospin transport ratio $R_i$ than the in-medium nucleon-nucleon cross sections, provided that the latter are constrained to a fixed total NN collision rate. We also explore both $DR(n/p)$ and $R_i$ as a function of the impact parameter. Since the copious production of intermediate mass fragments is a distinguishing feature of intermediate-energy heavy-ion collisions, we examine the isospin transport ratios constructed from different groups of fragments. We find that the values of the isospin transport ratios for projectile rapidity fragments with $Z\ge20$ are greater than those constructed from the entire projectile rapidity source. We believe experimental investigations of this phenomenon can be performed. These may provide significant tests of fragmentation time scales predicted by ImQMD calculations.Comment: 24 pages, 9 figures, to be published in Phys. Rev.

Transport Model Simulations of Projectile Fragmentation Reactions at 140 MeV/nucleon

The collisions in four different reaction systems using $^{40,48}$Ca and $^{58,64}$Ni isotope beams and a Be target have been simulated using the Heavy Ion Phase Space Exploration and the Antisymmetrized Molecular Dynamics models. The present study mainly focuses on the model predictions for the excitation energies of the hot fragments and the cross sections of the final fragments produced in these reactions. The effects of various factors influencing the final fragment cross sections, such as the choice of the statistical decay code and its parameters have been explored. The predicted fragment cross sections are compared to the projectile fragmentation cross sections measured with the A1900 mass separator. At $E/A=140$ MeV, reaction dynamics can significantly modify the detection efficiencies for the fragments and make them different from the efficiencies applied to the measured data reported in the previous work. The effects of efficiency corrections on the validation of event generator codes are discussed in the context of the two models.Comment: 28 pages, 13 figure

Determination of the reaction plane in ultrarelativistic nuclear collisions

In the particles produced in a nuclear collision undergo collective flow, the reaction plane can in principle be determined through a global event analysis. We show here that collective flow can be identified by evaluating the reaction plane independently in two separate rapidity intervals, and studying the correlation between the two results. We give an analytical expression for the correlation function between the two planes as a function of their relative angle. We also discuss how this correlation function is related to the anisotropy of the transverse momentum distribution. Email contact: [email protected]: Saclay-T93/026 Email: [email protected]

Photoexcited transients in disordered semiconductors: Quantum coherence at very short to intermediate times

We study theoretically electron transients in semiconductor alloys excited by light pulses shorter than 100 femtoseconds and tuned above the absorption edge during and shortly after the pulse, when disorder scattering is dominant. We use non-equilibrium Green functions employing the field-dependent self-consistent Born approximation. The propagators and the particle correlation function are obtained by a direct numerical solution of the Dyson equations in differential form. For the purely elastic scattering in our model system the solution procedures for the retarded propagator and for the correlation function can be decoupled.The propagator is used as an input in calculating the correlation function. Numerical results combined with a cumulant expansion permit to separate in a consistent fashion the dark and the induced parts of the self-energy. The dark behavior reduces to propagation of strongly damped quasi-particles; the field induced self-energy leads to an additional time non-local coherence. The particle correlation function is formed by a coherent transient and an incoherent back-scattered component. The particle number is conserved only if the field induced coherence is fully incorporated. The transient polarization and the energy balance are also obtained and interpreted.Comment: Accepted for publication in Phys. Rev. B; 37 pages,17 figure