Papers by M. Brandstetter
Progress in Particle and Nuclear Physics, 1998
Physical Review C, 2000
We study the local equilibrium in the central V = 125 fm 3 cell in heavy-ion collisions at energi... more We study the local equilibrium in the central V = 125 fm 3 cell in heavy-ion collisions at energies from 10.7A GeV (AGS) to 160A GeV (SPS) calculated in the microscopic transport model. In the present paper the hadron yields and energy spectra in the cell are compared with those of infinite nuclear matter, as calculated within the same model. The agreement between the spectra in the two systems is established for times t ≥ 10 fm/c in the central cell. The cell results do not deviate noticeably from the infinite matter calculations with rising incident energy, in contrast to the apparent discrepancy with predictions of the statistical model (SM) of an ideal hadron gas. The entropy of this state is found to be very close to the maximum entropy, while hadron abundances and energy spectra differ significantly from those of the SM.
Nuclear Physics A, 1999
The hypothesis of local equilibrium (LE) in relativistic heavy ion collisions at energies from AG... more The hypothesis of local equilibrium (LE) in relativistic heavy ion collisions at energies from AGS to RHIC is checked in the microscopic transport model. We find that kinetic, thermal, and chemical equilibration of the expanding hadronic matter is nearly reached in central collisions at AGS energy for t ≥ 10 fm/c in a central cell. At these times the equation of state may be approximated by a simple dependence P ∼ = (0.12 − 0.15) ε. Increasing deviations of the yields and the energy spectra of hadrons from statistical model values are observed for increasing bombarding energies. The origin of these deviations is traced to the irreversible multiparticle decays of strings and many-body (N ≥ 3) decays of resonances. The violations of LE indicate that the matter in the cell reaches a steady state instead of idealized equilibrium. The entropy density in the cell is only about 6% smaller than that of the equilibrium state.
Journal of Physics G: Nuclear and Particle Physics, 1999
Thermodynamical variables and their time evolution are studied for central relativistic heavy ion... more Thermodynamical variables and their time evolution are studied for central relativistic heavy ion collisions from 10.7 to 160 AGeV in the microscopic Ultrarelativistic Quantum Molecular Dynamics model (UrQMD). The UrQMD model exhibits drastic deviations from equilibrium during the early high density phase of the collision. Local thermal and chemical equilibration of the hadronic matter seems to be established only at later stages of the quasi-isentropic expansion in the central reaction cell with volume 125 fm 3 . Baryon energy spectra in this cell are reproduced by Boltzmann distributions at all collision energies for t ≥10 fm/c with a unique rapidly dropping temperature. At these times the equation of state has a simple form: P ∼ = (0.12 − 0.15) ε. At SPS energies the strong deviation from chemical equilibrium is found for mesons, especially for pions, even at the late stage of the reaction. The final enhancement of pions is supported by experimental data.
Kollektive Effekte in heißer und dichter Kernmaterie
Uploads
Papers by M. Brandstetter