Covariant transport approach for heavy-ion reactions

doi:10.1016/0375-9474(92)90453-Q

Nuclear Physics A

Volume 545, Issues 1–2, 3 August 1992, Pages 123-138

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Abstract

The description of heavy-ion collisions up to bombarding energies of a few GeV per nucleon is based on a relativistic transport equation for the baryon phase-space distribution as derived from time-dependent Dirac-Bruecker theory within semiclassical limits. It describes the selfconsistent mean-field dynamics with its momentum-dependent forces as well as the residual nucleon-nucleon collisional history. We analyze the sensitivity of flow observables to the scalar and vector part of the nucleon selfenergy and try to extract information on the nuclear equation of state (EOS) in comparison with experimental data. Furthermore, we calculate K⁺ spectra for Ne + Ne and Au + Au at 1 GeV/u and compare to the recent data from the SIS since K⁺ cross sections exhibit a sizeable sensitivity to the EOS. In the last part of this contribution we provide predictions for antiproton spectra from nucleus-nucleus collisions accounting for the in-medium modification of the nucleon mass.

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The production of antiprotons in p+A reactions is calculated in a microscopic transport approach employing hadronic and string degrees of freedom (HSD). It is found that the abundancies of antiprotons as observed by the E910 Collaboration in p+A reactions at 12.3 GeV/c as well as 17.5 GeV/c can approximately be described on the basis of primary proton–nucleon and secondary meson–baryon production channels for all targets. The transport calculations demonstrate that the antiproton rapidity distributions for heavy targets are sensitive to the $p ̄$ (or hadron) formation time in the nuclear medium. Within our analysis the data from the E910 Collaboration are reasonably described with a formation time of 0.4–0.8 fm/c in the hadron rest frame.
Antibaryon production in hot and dense nuclear matter
2002, Nuclear Physics A
The production of antibaryons is calculated in a microscopic transport approach employing multiple-meson fusion reactions according to detailed balance relations with respect to baryon–antibaryon annihilation. It is found that the abundancies of antiprotons as observed from peripheral to central collisions of Pb+Pb at the SPS and Au+Au at the AGS can approximately be described on the basis of multiple interactions of ‘formed’ hadronic states which drive the system to chemical equilibrium by flavor exchange or quark rearrangement reactions.
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1999, Physics Report
We review the constraints imposed by the spontaneously broken chiral symmetry of the QCD vacuum on the hadron properties at finite temperature T and baryon density ρ_B. A restoration of chiral symmetry is indicated by the dropping of the scalar quark condensate $q ̄ q$ at finite T and ρ_B in various approaches. This suggests the hadrons to become approximately massless in hot and dense nuclear matter or the vector and axial vector currents to become equal. In this respect we study the properties of hadrons – as produced in relativistic nucleus–nucleus collisions – by means of a covariant hadronic transport approach where scalar and vector hadron self-energies are taken into account explicitly which are modelled in terms of effective ‘chiral’ Lagrangians. Within this transport approach we investigate the reaction dynamics of relativistic heavy-ion collisions and analyse experimental data on $π, η, K^{+}, K^{−}, ρ, ω, φ, p ̄$ and charmonium production for proton–nucleus and nucleus–nucleus collisions from SIS to SPS energies (1–200A GeV). Whereas $π, η$ and to some extent K⁺ mesons are found not to change their properties in the nuclear medium substantially, antiprotons and antikaons do show sizeable attractive self-energies as can be extracted from their experimental abundancies and spectra. The properties of the vector mesons $ρ, ω$ and φ at finite baryon density are investigated by their dileptonic decay; the CERES and HELIOS-3 data at SPS energies are found to be incompatible with a ‘bare’ vector meson mass scenario. Here, a description by ‘dropping’ ρ and ω masses leads to a very good reproduction of the data, however, also approaches based on more conventional hadronic interactions as pion polarizations and meson–nucleon scattering amplitudes are compatible with the present dilepton spectra at SPS energies. Constraints from dilepton studies at BEVALAC/SIS energies are investigated in all decay schemes as well as a variety of further observables that allow to disentangle the different scenarios experimentally. Furthermore, the charmonium production and suppression in proton–nucleus and nucleus–nucleus collisions is investigated within the transport approach in order to probe a possible transition to a quark-gluon plasma (QGP) phase. We finally discuss ‘optimized’ observables for an experimental investigation of the restoration of chiral symmetry and/or the phase transition to a quark-gluon plasma.
Reanalysis of antiproton production in proton-nucleus and nucleus-nucleus reactions at subthreshold energies
1998, Nuclear Physics A
We reanalyse the production of $p p$ pairs in proton-nucleus and nucleus-nucleus collisions employing novel elementary cross sections for baryon-baryon and pion-baryon production channels based on a boson-exchange model. In contrast to previous transport studies performed in the literature the secondary pion induced channel is found to be most important in both p + A and A + A collisions at subthreshold energies. A detailed comparison with the experimental data available indicates that sizeable attractive $p$ potentials in the order of −100 to −150 MeV at normal nuclear matter density are needed to reproduce the size and shape of the experimental spectra.
Analysis of kaon production at SIS energies
1997, Nuclear Physics A
We analyse the production and propagation of pions and kaons in heavy-ion reactions from 0.8–1.8 A GeV within a coupled channel transport approach including the kaon production channels BB → K⁺YN, πB → K⁺Y, $BB → NNK K$ , $πB → NK K$ , K⁺B → K⁺B, and $ππ → K K$ . Assuming the hyperon self-energy to be $23$ of the nucleon self-energy we find that all inclusive experimental K⁺ spectra at SIS energies can be reproduced reasonably well without any self-energies for the kaons although a slightly repulsive kaon potential cannot be excluded by the present data on kaon spectra and flow.
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We analyse the production and propagation of kaons and antikaons in Ni + Ni reactions from 0.8–1.85 GeV/u within a coupled channel transport approach including the channels BB → K⁺YN, πB → K⁺Y, $BB → NNK K$ , $πB → NK K$ , K⁺B → K⁺B, $K B → K B$ , $YN → K NN$ , $ππ → K K$ as well as $πY → K N$ and $K N → πY$ for the antikaon absorption. Whereas the experimental K⁺ spectra can be reproduced without introducing any self-energies for the mesons in Ni + Ni collisions from 0.8 to 1.8 GeV/u, the K⁻ yield is underestimated by a factor of 5–7 at 1.66 and 1.85 GeV/u. However, introducing density dependent antikaon masses in line with effective chiral Lagrangians, the antikaon spectra can be reasonably well described.

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^☆: Supported by BMFT and GSI Darmstadt

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Covariant transport approach for heavy-ion reactions☆

Abstract

Phys. Rep.

Phys. Rep.

Phys. Rep.

Phys. Rep.

Prog. Part. Nucl. Phys.

Phys. Rep.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Phys. Lett.

Z. Phys.

Phys. Lett.

Phys. Rev.

Phys. Lett.

Phys. Rev. Lett.

Phys. Rev.

Phys. Rev.

Phys. Rev.

Phys. Rev.