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

Proton-nucleus reactions are discussed in the framework of the evolution model proposed by Hwa. The longitudinal-momentum distributions of baryons are calculated and compared with the data. A momentum-degradation length of 5.7 to 6.9 fm is found. These results are contrasted with other recent theoretical analyses. The implication is that the central cores of heavy nuclei such as U and Pb may stop each other at beam energies up to 25 GeV per nucleon.

Deceleration of high-energy protons by heavy nuclei

Fragment yields and phase coexistence in nuclear collisions

Transverse-momentum data are analyzed for the presence of collective flow of nuclear matter in interactions of Au and Xe in nuclear emulsion at energies from 0.5 to 1.2 GeV/nucleon. Evidence of such flow is obtained from 122 interactions involving AgBr in nuclear emulsion by adapting a recently proposed method of transverse-momentum analysis.

Identification of collective flow by transverse-momentum analysis of emulsion data for Au+AgBr and Xe+AgBr.

The final states of central Ca + Ca and Nb + Nb collisions at 400 and 1050 MeV/nucleon and at 400 and 650 MeV/nucleon, respectively, are studied with two independently developed statistical models, namely the classical microcanonical model and the quantum-statistical grand canonical model. It is shown that these models are in agreement with each other for these systems. Furthermore, it is demonstrated that there is essentially a one-to-one relationship between the observed relative abundances of the light fragments p, d, t, $^{3}\mathrm{He}$, and \ensuremath{\alpha} and the entropy per nucleon, for breakup temperatures greater than 30 MeV. Entropy values of 3.5--4 are deduced from high-multiplicity selected fragment yield data.

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Quantitative analysis of the relation between entropy and nucleosynthesis in central Ca + Ca and Nb + Nb collisions

In a fluid-dynamical model, the extra entropy production which arises from a nonequilibrium phase transition from nuclear to quark-gluon matter is calculated.

L. P. Csernai

Papers

Deceleration of high-energy protons by heavy nuclei

Fragment yields and phase coexistence in nuclear collisions

Identification of collective flow by transverse-momentum analysis of emulsion data for Au+AgBr and Xe+AgBr.

Quantitative analysis of the relation between entropy and nucleosynthesis in central Ca + Ca and Nb + Nb collisions

Extra entropy production due to nonequilibrium phase transitions in relativistic heavy ion reactions.