Baryon stopping and particle production in Pb+Pb collisions at 158 GeV/nucleon are studied as a function of the collision centrality using new proton, antiproton, charged kaon and charged pion production data measured with the NA49 experiment at the CERN Super Proton Synchrotron (SPS). Stopping, which is measured by the shift in rapidity of net protons or baryons from the initial beam rapidity, increases in more central collisions. This is expected from a geometrical picture of the collisions. The stopping data are quantitatively compared to models incorporating various mechanisms for stopping. In general, microscopic transport calculations which incorporate current theoretical models of baryon stopping or use phenomenological extrapolations from simpler systems overestimate the dependence of stopping on centrality. Approximately, the yield of produced pions scales with the number of nucleons participating in the collision. A small increase in yield beyond this scaling, accompanied by a small suppression in the yield of the fastest pions, reflects the variation in stopping with centrality. Consistent with the observations from central collisions of light and heavy nuclei at the SPS, the transverse momentum distributions of all particles are observed to become harder with increasing centrality. This effect is most pronounced for the heaviest particles. This hardening is discussed in terms of multiple scattering of the incident nucleons of one colliding nucleus as they traverse the other nucleus and in terms of rescattering within the system of produced particles.

The 1997 International Europhysics Conference on High Energy Physics was held at the campus of the Hebrew University of Jerusalem and at the Jerusalem Renaissance Hotel, from August 19th to August 25th, 1997. This was the first time that the European Physical Society had its High Energy Physics Conference outside the boundary of Europe. A total of 550 physicists participated in the conference with a total of 250 presentations in the parallel sessions and 26 presentations in the plenary sessions. The Board of the of the High Energy and Particle Physics division (HEPP) of the EPS acted as the Scientific Organizing Committee. The Board acknowl edges the help of the International Advisory Committee as well as that of the Local Organizing Committee. The conference was co-organized by the Hebrew University of Jerusalem and by the Weizmann Institute of Science, with important help by physi cists from the Israeli Institute of Technology (Technion) and the Tel Aviv University.

This thesis presents theoretical and numerical studies on phenomenological description of the quark–gluon plasma (QGP), a many-body system of elementary particles. The author formulates a causal theory of hydrodynamics for systems with net charges from the law of increasing entropy and a momentum expansion method. The derived equation results can be applied not only to collider physics, but also to the early universe and ultra-cold atoms. The author also develops novel off-equilibrium hydrodynamic models for the longitudinal expansion of the QGP on the basis of these equations. Numerical estimations show that convection and entropy production during the hydrodynamic evolution are key to explaining excessive charged particle production, recently observed at the Large Hadron Collider. Furthermore, the analyses at finite baryon density indicate that the energy available for QGP production is larger than the amount conventionally assumed.