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  • Dumitru, Adrian Bogdan (38)
  • Stöcker, Horst (36)
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  • heavy ion collisions (5)
  • heavy-ion collisions (5)
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  • Physik (38)
  • Frankfurt Institute for Advanced Studies (FIAS) (4)
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Pion and thermal photon spectra as a possible signal for a phase transition (2005)
Dumitru, Adrian Bogdan ; Katscher, Ulrich ; Maruhn, Joachim ; Stöcker, Horst ; Greiner, Walter ; Rischke, Dirk-Hermann
We calculate thermal photon and neutral pion spectra in ultrarelativistic heavy-ion collisions in the framework of three-fluid hydrodynamics. Both spectra are quite sensitive to the equation of state used. In particular, within our model, recent data for S + Au at 200 AGeV can only be understood if a scenario with a phase transition (possibly to a quark-gluon plasma) is assumed. Results for Au+Au at 11 AGeV and Pb + Pb at 160 AGeV are also presented.
Thermal photons as a measure for the rapidity dependence of the temperature (1995)
Dumitru, Adrian Bogdan ; Katscher, Ulrich ; Maruhn, Joachim ; Stöcker, Horst ; Greiner, Walter ; Rischke, Dirk-Hermann
The rapidity distribution of thermal photons produced in Pb+Pb collisions at CERN-SPS energies is calculated within scaling and three- fluid hydrodynamics. It is shown that these scenarios lead to very different rapidity spectra. A measurement of the rapidity dependence of photon radiation can give cleaner insight into the reaction dynamics than pion spectra, especially into the rapidity dependence of the temperature.
Suppression of dilepton production at finite baryon density (1993)
Dumitru, Adrian Bogdan ; Rischke, Dirk-Hermann ; Schönfeld, Thomas ; Winckelmann, Luke Andreas ; Stöcker, Horst ; Greiner, Walter
We study dilepton production from a quark-gluon plasma of given energy density at finite quark chemical potential μ and find that the dilepton production rate is a strongly decreasing function of μ. Therefore, the signal to background ratio of dileptons from a plasma created in a heavy-ion collision may decrease significantly.
Nucleus-nucleus collisions at highest energies (1996)
Bleicher, Marcus ; Amelin, Nikolai ; Bass, Steffen A. ; Brandstetter, Mathias ; Dumitru, Adrian Bogdan ; Ernst, Christoph ; Gerland, Lars ; Konopka, Jens ; Spieles, Christian ; Weber, Henning ; Winckelmann, Luke Andreas ; Stöcker, Horst ; Greiner, Walter
The microscopic phasespace approach URQMD is used to investigate the stopping power and particle production in heavy systems at SPS and RHIC energies. We find no gap in the baryon rapidity distribution even at RHIC. For CERN energies URQMD shows a pile up of baryons and a supression of multi-nucleon clusters at midrapidity.
Hypermatter : properties and formation in relativistic nuclear collisions (1995)
Gerland, Lars Arne ; Spieles, Christian ; Bleicher, Marcus ; Papazoglou, Panajotis ; Brachmann, Jörg ; Dumitru, Adrian Bogdan ; Stöcker, Horst ; Greiner, Walter ; Schaffner, Jürgen ; Greiner, Carsten
The extension of the Periodic System into hitherto unexplored domains - anti- matter and hypermatter - is discussed. Starting from an analysis of hyperon and single hypernuclear properties we investigate the structure of multi-hyperon objects (MEMOs) using an extended relativistic meson field theory. These are contrasted with multi-strange quark states (strangelets). Their production mechanism is stud- ied for relativistic collisions of heavy ions from present day experiments at AGS and SPS to future opportunities at RHIC and LHC. It is pointed out that abso- lutely stable hypermatter is unlikely to be produced in heavy ion collisions. New attention should be focused on short lived metastable hyperclusters ( / 10 10s) and on intensity interferometry of multi-strange-baryon correlations.
Density perturbations in heavy- ion collisions below the critical point (2004)
Dumitru, Adrian Bogdan ; Paech, Kerstin ; Stöcker, Horst
Universality arguments suggest that the chiral phase transition for two massless quark flavors is second-order at baryon-chemical potential µB = 0 [1], which then becomes a crossover for small quark masses.
Physics opportunities at RHIC and LHC (1999)
Scherer, Stefan ; Bass, Steffen A. ; Belkacem, Mohamed ; Bleicher, Marcus ; Brachmann, Jörg ; Dumitru, Adrian Bogdan ; Ernst, Christoph ; Gerland, Lars ; Hammon, Nils ; Hofmann, Markus ; Konopka, Jens ; Neise, Ludwig ; Reiter, Manuel ; Schramm, Stefan ; Soff, Sven ; Spieles, Christian ; Weber, Henning ; Zschiesche, Detlef ; Maruhn, Joachim ; Stöcker, Horst ; Greiner, Walter
Nonequilibrium models (three-fluid hydrodynamics, UrQMD, and quark molecular dynamics) are used to discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions from the SPS via RHIC to LHC. It is demonstrated that these models - although they do treat the most interesting early phase of the collisions quite differently (thermalizing QGP vs. coherent color fields with virtual particles) -- all yield a reasonable agreement with a large variety of the available heavy ion data. Hadron/hyperon yields, including J/Psi meson production/suppression, strange matter formation, dileptons, and directed flow (bounce-off and squeeze-out) are investigated. Observations of interesting phenomena in dense matter are reported. However, we emphasize the need for systematic future measurements to search for simultaneous irregularities in the excitation functions of several observables in order to come close to pinning the properties of hot, dense QCD matter from data. The role of future experiments with the STAR and ALICE detectors is pointed out.
Fluctuations and inhomogenities of energy density and isospin in Pb + Pb at the SPS (1998)
Bleicher, Marcus ; Gerland, Lars ; Spieles, Christian ; Dumitru, Adrian Bogdan ; Bass, Steffen A. ; Belkacem, Mohamed ; Brandstetter, Mathias ; Ernst, Christoph ; Neise, Ludwig ; Soff, Sven ; Weber, Henning ; Stöcker, Horst ; Greiner, Walter
The main goal of heavy ion physics in the last fifteen years has been the search for the quark-gluon-plasma(QGP). Until now, unambigous experimental evidence for the QGP is missing.
Direct photons in Pb+Pb at CERN-SPS from microscopic transport theory (1997)
Dumitru, Adrian Bogdan ; Bleicher, Marcus ; Bass, Steffen A. ; Spieles, Christian ; Neise, Ludwig ; Stöcker, Horst ; Greiner, Walter
Direct photon production in central Pb+Pb collisions at CERN-SPS energy is calculated within the relativistic microscopic transport model UrQMD, and within distinctly di erent versions of relativistic hydrodynamics. We find that in UrQMD the local momentum distributions of the secondaries are strongly elongated along the beam axis initially. Therefore, the preequilibrium contribution dominates the photon spectrum at transverse momenta above H 1.5 GeV. The hydrodynamics prediction of a strong correlation between the temperature and radial expansion velocities on the one hand and the slope of the transverse momentum distribution of direct photons on the other hand thus is not recovered in UrQMD. The rapidity distribution of direct photons in UrQMD reveals that the initial conditions for the longitudinal expansion of the photon source (the meson fluid ) resemble rather boostinvariance than Landau-like flow.
Probes for the early reaction dynamics of heavy ion collisions at AGS and SPS (1997)
Dumitru, Adrian Bogdan ; Brachmann, Jörg ; Bleicher, Marcus ; Maruhn, Joachim ; Stöcker, Horst ; Greiner, Walter
We discuss the early evolution of ultrarelativistic heavy-ion collisions within a multi- fluid dynamical model. In particular, we show that due to the finite mean-free path of the particles compression shock waves are smeared out considerably as compared to the one-fluid limit. Also, the maximal energy density of the baryons is much lower. We discuss the time scale of kinetic equilibration of the baryons in the central region and its relevance for directed flow. Finally, thermal emission of direct photons from the fluid of produced particles is calculated within the three-fluid model and two other simple expansion models. It is shown that the transverse momentum and rapidity spectra of photons give clue to the cooling law and the early rapidity distribution of the photon source.
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