Direct photons in Pb+Pb at CERN-SPS from microscopic transport theory

  • 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.

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Author:Adrian Bogdan DumitruORCiDGND, Marcus BleicherORCiDGND, Steffen A. BassORCiDGND, Christian Spieles, Ludwig NeiseGND, Horst StöckerORCiDGND, Walter GreinerGND
Document Type:Preprint
Date of Publication (online):2005/12/15
Year of first Publication:1997
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2005/12/15
Tag:Kollisionen schwerer Ionen; Quanten-Molekular-Dynamik; SPS; UrQMD
Quanten-Molekular-Dynamic; SPS; UrQMD; heavy-ion collisions
Source:Report-no: UFTP 449/1997, Phys.Rev.C57:3271-3275,1998,
Institutes:Physik / Physik
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 53 Physik / 530 Physik
Licence (German):License LogoDeutsches Urheberrecht