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Thermal dileptons from coarse-grained transport as fireball probes at SIS energies

  • Tetyana Galatyuk
  • Paul M. Hohler
  • Ralf Rapp
  • Florian Seck
  • Joachim Stroth
Regular Article - Theoretical Physics

Abstract.

Utilizing a coarse-graining method to convert hadronic transport simulations of Au+Au collisions at SIS energies into local temperature, baryon and pion densities, we compute the pertinent radiation of thermal dileptons based on an in-medium \( \rho\) spectral function that describes available spectra at ultrarelativistic collision energies. In particular, we analyze how far the resulting yields and slopes of the invariant-mass spectra can probe the lifetime and temperatures of the fireball. We find that dilepton radiation sets in after the initial overlap phase of the colliding nuclei of about 7fm/c, and lasts for about 13fm/c. This duration closely coincides with the development of the transverse collectivity of the baryons, thus establishing a direct correlation between hadronic collective effects and thermal EM radiation, and supporting a near local equilibration of the system. This fireball “lifetime” is substantially smaller than the typical 20-30fm/c that naive considerations of the density evolution alone would suggest. We furthermore find that the total dilepton yield radiated into the invariant-mass window of \( M=0.3\) -0.7GeV/c^2 normalized to the number of charged pions, follows a relation to the lifetime found earlier in the (ultra-) relativistic regime of heavy-ion collisions, and thus corroborates the versatility of this tool. The spectral slopes of the invariant-mass spectra above the \( \phi\) -meson mass provide a thermometer of the hottest phases of the collision, and agree well with the maximal temperatures extracted from the coarse-grained hadron spectra.

Keywords

Baryon Density Dilepton Production Dilepton Spectrum HADES Collaboration Nuclear Saturation Density 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© SIF, Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • Tetyana Galatyuk
    • 1
    • 2
  • Paul M. Hohler
    • 3
  • Ralf Rapp
    • 3
  • Florian Seck
    • 1
    • 2
  • Joachim Stroth
    • 3
    • 2
  1. 1.Technische Universität DarmstadtDarmstadtGermany
  2. 2.GSI Helmholtzzentrum für Schwerionenforschung GmbHDarmstadtGermany
  3. 3.Texas A&M UniversityCollege StationUSA

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