Bochum 1998 – scientific programme

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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 (p_t=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 µ_B). 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 µ_B 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