Studies of Nuclear Matter under Extreme Conditions: Heavy-Ion Interactions at Ultra-Relativistic Energies

Sammanfattning: The charged particle production in ultra-relativistic nucleus-nucleus collisions in the energy range 4-200 A GeV has been studied. Two different experimental techniques have been utilized: nuclear emulsions and Multi-Step Avalanche Chambers. Four large Multi-Step Avalanche Chambers with optical read-out were included in the experiment WA93 and were used to reconstruct the tracks and determine the momenta of negatively charged particles. The performance of the chambers in the experiment as well as the analysis of the chamber data are described in the thesis. The reconstructed particle momenta have been used to study transverse momentum distributions of negatively charged particles, and to perform intensity interferometry analyses (HBT) in order to determine the source size and study the time-evolution of the interactions. The transverse momentum spectra can not be fitted to a single thermal distribution over the full transverse momentum range. Furthermore, the shapes of the transverse momentum spectra are found to be different in central and peripheral nucleus-nucleus collisions. The invariant radius extracted from the interferometry analysis decreases with increasing transverse momenta of the particle pairs, indicating an expanding source. The multiplicity and pseudorapidity distributions obtained from interactions in nuclear emulsion have been studied. Simulations have been performed with various Monte-Carlo models, and particularly the effects of the hadronic rescattering have been investigated. The results of the analysis have illustrated the great importance of the nuclear geometry in ultra-relativistic nucleus-nucleus collisions. The pseudorapidity distributions of produced particles have been found to be well described by gaussian functions. Based on gaussian parameterizations a method of predicting the pseudorapidity distributions in systems of different sizes and at different energies has been developed. Furthermore, the multiplicity and angular distributions of slow, target associated particles have been analysed.