E. L. Bratkovskaya

Hadronic and electromagnetic probes of hot and dense nuclear matter

Abstract 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 ρB. A restoration of chiral symmetry is indicated by the dropping of the scalar quark condensate q q at finite T and ρB 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 (1–200Axa0GeV). 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.

Kaon versus antikaon production at SIS energies

Abstract 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.

Strangeness dynamics and transverse pressure in relativistic nucleus-nucleus collisions

We investigate hadron production as well as transverse hadron spectra from proton-proton, proton-nucleus and nucleus-nucleus collisions from 2

Analysis of kaon production at SIS energies

Acdot

Hadronic observables at relativistic energies: Anything strange with strangeness?

GeV to 21.3

Charmonium suppression with cc̄ dissociation by strings1

Acdot

Kaons and antikaons in hot and dense hadronic matter

TeV within two independent transport approaches (HSD and UrQMD) that are based on quark, diquark, string and hadronic degrees of freedom. The comparison to experimental data on transverse mass spectra from

Low-mass dileptons and dropping rho meson mass

pp

Meson mT-scaling in heavy-ion collisions at SIS energies

,

Dilepton anisotropy from p + Be and Ca + Ca collisions at BEVALAC energies

pA