A schematic model for fragmentation and phase transition in nuclear collisions

We develop here a simple yet versatile model for nuclear fragmentation in heavy ion collisions. The model allows us to calculate thermodynamic properties such as phase transitions as well as the distribution of fragments at disassembly. In spite of its simplicity the model gives very good fit to recent data taken at the Michigan National Superconducting Cyclotron Laboratory. The model is an extension of a lattice gas model which itself has strong overlaps with percolation models which have been used in the past to compare with nuclear fragmentation data.Comment: 12 pages (RevTex), 4 figures (uuencoded ps file), To appear in Phys. Lett.

Cluster Production with Coalescence and Breakup

The problem of hadronic cluster production in quark-hadron phase transition in heavy-ion collisions is studied by cellular automata. Previous result on the scaling behavior is extended to include variation in the drift speed. It is also shown that coalescence is more important than growth in generating scaling. A new set of rules is adopted to free the clusters from being rigid. It is found that the scaling exponent is independent of not only the shapes of the clusters, but also the probability of breakup of the clusters. The universality of the scaling behavior is now extended to a wide range of physical properties characterizing the geometry and dynamics of the phase transition process.Comment: 8 pages, Latex, 9 figures in ps files, submitted to Phys. Rev.

Lattice gas model for fragmentation: From Argon on Scandium to Gold on Gold

The recent fragmentation data for central collisions of Gold on Gold are even qualitatively different from those for central collisions of Argon on Scandium. The latter can be fitted with a lattice gas model calculation. Effort is made to understand why the model fails for Gold on Gold. The calculation suggests that the large Coulomb interaction which is operative for the larger system is responsible for this discrepancy. This is demonstrated by mapping the lattice gas model to a molecular dynamics calculation for disassembly. This mapping is quite faithful for Argon on Scandium but deviates strongly for Gold on Gold. The molecular dynamics calculation for disassembly reproduces the characteristics of the fragmentation data for both Gold on Gold and Argon on Scandium.Comment: 13 pages, Revtex, 8 figures in ps files, submitted to Phys. Rev.

Cluster Growth in Two-Dimensional Quark-Hadron Phase Transition

The problem of hadronic cluster production in heavy-ion collisions is studied in search for an observable signature of first-order quark-hadron phase transition. The study is carried out by cellular automata in a two-dimensional model of the mixed phase at midrapidity. The clusters are allowed to grow as well as to coalesce upon collision. The distribution of cluster sizes is found to exhibit scaling behavior that is independent of the size of the mixed region, nucleation radius and nucleation probability. The universal scaling index $\gamma=1.86\pm 0.18$ may be used to characterize and identify the phase transition process. Possible connection with self-organized criticality is pointed out.Comment: 14 pages, 9 postscript figures include

Cluster Production in Quark-Hadron Phase Transition

The problem of cluster formation and growth in first-order quark-hadron phase transition in heavy-ion collisions is considered. Behaving as Brownian particles, the clusters carry out random walks and can encounter one another, leading to coalescence and breakup. A simulation of the process in cellular automaton suggests the possibility of a scaling distribution in the cluster sizes. The experimental determination of the cluster-size distribution is urged as a means to find a clear signature of phase transition.Comment: 12 pages + 1 figure. Report # OITS-517. To be published in Phys. Rev. Lett. 71, xxx (1994

First Order Phase Transition in Intermediate Energy Heavy Ion Collisions

We model the disassembly of an excited nuclear system formed as a result of a heavy ion collision. We find that, as the beam energy in central collisions in varied, the dissociating system crosses a liquid-gas coexistence curve, resulting in a first-order phase transition. Accessible experimental signatures are identified: a peak in specific heat, a power-law yield for composites, and a maximum in the second moment of the yield distribution

A unified description for nuclear equation of state and fragmentation in heavy ion collisions

We propose a model that provides a unified description of nuclear equation of state and fragmentations. The equation of state is evaluated in Bragg-Williams as well as in Bethe-Peierls approximations and compared with that in the mean field theory with Skyrme interactions. The model shows a liquid-gas type phase transition. The nuclear fragment distributions are studied for different densities at finite temperatures. Power law behavior for fragments is observed at critical point. The study of fragment distribution and the second moment $S_2$ shows that the thermal critical point coincides with the percolation point at the critical density. High temperature behavior of the model shows characteristics of chemical equilibrium.Comment: 20 pages in RevTex, 11 figures (uuencoded ps files), to appear in Phys. Rev.

Probing quark gluon plasma with jets

We study multiple scatterings of jets on constituents of quark gluon plasma and introduce energy--energy correlations to quantify their effects. The effects from a longitudinally expanding plasma on medium as well as high energy jets are found to be significant at both RHIC and LHC energies. Because jets escape from the plasma long before the completion of mixed phase, these effects are free from complications of final state hadronic interactions and decays. These suggest that jets can be used to probe the plasma that might be created in future high energy heavy ion collisions.Comment: 15 pages, 6 figures in 5 ps files included, McGill/94-1