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HK: Hadronen und Kerne
HK 34: Heavy Ion Reactions IV, Relativistic Energies
HK 34.6: Talk
Tuesday, March 17, 1998, 18:45–19:00, P
A Thermal Concept for Heavy Ion Collisions at Relativistic Energies[*] — •A. Förster — Technische Universität Darmstadt
Using the Kaon Spectrometer at SIS (GSI) charged pion spectra have been measured up to high momenta (pt=0.9 GeV/c) for symmetric collision systems from A = 12 to 197 at incident energies between 0.6 and 2 A·GeV. The spectra deviate from a pure Boltzmann shape exhibiting an enhancement at low momenta.
In order to describe the shape of the pion spectra we apply a thermal concept. We consider a system of nucleons, excited baryonic resonances (in particular Δ(1232) and N*(1440)) and pions in thermal and chemical equilibrium (T and µB). This system expands with a flow velocity (β). In this concept all particles freeze out at the same time. The pion spectrum consists of “thermal” pions and those from resonance decay. The values of T and β are taken from proton and fragment energy distributions and µB is derived by fitting the fraction of thermal pions. This procedure has been applied for Au+Au collisions at 1 A·GeV and C+C collisions at 1 and 2 A·GeV.
Further, a simple attempt to describe the spectral shape by continous pion emission from a cooling source will be discussed.
[*] gefördert von BMBF und GSI