A guide to microscopic models for intermediate energy heavy ion collisions

Statistical multifragmentation of nuclei

Recent studies based on lattice Monte Carlo simulations of quantum chromodynamics (QCD)—the theory of strong interactions—have demonstrated that at high temperature there is a phase change from confined hadronic matter to a deconfined quark–gluon plasma in which quarks and gluons can travel distances that greatly exceed the size of hadrons. Here we show that the phase structure of such strongly interacting matter can be decoded by analysing particle production in high-energy nuclear collisions within the framework of statistical hadronization, which accounts for the thermal distribution of particle species. Our results represent a phenomenological determination of the location of the phase boundary of strongly interacting matter, and imply quark–hadron duality at this boundary. By analysing particle production in high-energy nuclear collisions, the phase boundary of strongly interacting matter is located and the phase structure of quantum chromodynamics is elucidated, implying quark–hadron duality.

Decoding the phase structure of QCD via particle production at high energy

We present strange particle spectra and yields measured at midrapidity in √s=200 GeV proton-proton (p+p) collisions at the BNL Relativistic Heavy Ion Collider (RHIC). We find that the previously observed universal transverse mass (m_T≡√pT2+m2) scaling of hadron production in p+p collisions seems to break down at higher mT and that there is a difference in the shape of the mT spectrum between baryons and mesons. We observe midrapidity antibaryon to baryon ratios near unity for Λ and Ξ baryons and no dependence of the ratio on transverse momentum, indicating that our data do not yet reach the quark-jet dominated region. We show the dependence of the mean transverse momentum ⟨pT⟩ on measured charged particle multiplicity and on particle mass and infer that these trends are consistent with gluon-jet dominated particle production. The data are compared with previous measurements made at the CERN Super Proton Synchrotron and Intersecting Storage Rings and in Fermilab experiments and with leading-order and next-to-leading-order string fragmentation model predictions. We infer from these comparisons that the spectral shapes and particle yields from p+p collisions at RHIC energies have large contributions from gluon jets rather than from quark jets.

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Strange particle production in p+p collisions at s=200 GeV

Collective interactions in the preequilibrium quark matter and hadronic resonance gas stage of ultrarelativistic nucleus-nucleus collisions are studied in the framework of the transport theoretical approach RQMD. The paper reviews string fusion into color ropes and hadronic rescattering which serve as models for these interactions. Hadron production in central Pb(160A GeV) on Pb collisions has been calculated. The changes of the final flavor composition are more pronounced than in previous RQMD studies of light ion induced reactions at 200A GeV. The ratio of created quark pairs ss\ifmmode\bar\else\textasciimacron\fi{}/(u\ifmmode \bar{u}\else \={u}\fi{}+dd\ifmmode\bar\else\textasciimacron\fi{}) is enhanced by a factor of 2.4 in comparison to pp results. Color rope formation increases the initially produced antibaryons to 3 times the value in the ``NN mode,'' but only one quarter of the produced antibaryons survives because of subsequent strong absorption. The differences in the final particle composition for Pb on Pb collisions compared to S-induced reactions are attributed to the hadronic resonance gas stage which is baryon-richer and lasts longer.

Flavor production in Pb(160 A GeV) on Pb collisions: Effect of color ropes and hadronic rescattering

Entropy and cluster production in nuclear collisions

Inclusive cross sections for the reactions $p+A\ensuremath{\rightarrow}p+X$ at 100 GeV are discussed in the framework of the evolution model proposed by Hwa. An exact solution to the evolution equation is found. A momentum-degradation length of 4.9 fm is inferred from the data.

Proton stopping power of heavy nuclei

The transition from nuclear matter to quark matter in shock fronts is discussed. The relativistic shock equations are considered and applied to quark-matter production in dependence on the bag constant. The problem of shock splitting is discussed as a possible signature of the phase transition. One-dimensional hydrodynamical calculations for a two-phase system of nuclear matter and quark plasma are presented and compared to results of the shock equations for stable and unstable shock fronts.

L. P. Csernai

Papers

Entropy and cluster production in nuclear collisions

Proton stopping power of heavy nuclei

Stability of detonation fronts leading to quark-gluon plasma

On the relativistic hydrodynamical description of energetic heavy-ion reactions

Dynamical aspects of the transition from nuclear matter to a quark-gluon plasma in heavy ion collisions☆