Miroslaw Marek Kielbowicz

New results on energy and momentum conservation for particle emission in A+A collisions at not too high energies

We construct a new, simple model of the heavy ion collision. This model is local in the impact parameter plane and appropriate for the CERN Super Proton Synchrotron (SPS) energy range. It can be regarded as a new realization of the “fire-streak” approach, originally applied to studies of lower energy reactions. Starting from local energy and momentum conservation, we nicely describe the whole centrality dependence of the pion rapidity distribution in Pb+Pb collisions at √sNN =17.3 GeV. In particular we explain the broadening of the pion rapidity distribution when going from central to peripheral collisions. The results of our calculations are compared to experimental data from the NA49 detector at the SPS. We discuss the resulting implications on the role played by energy and momentum conservation for the dynamics of particle production in the heavy ion collision. We conclude that the latter conservation laws play a dominant role in the centrality dependence of the absolute size and shape of pion rapidity spectra. A specific space-time picture emerges, where the longitudinal evolution of the system strongly depends on the position in the impact parameter (bx, by) plane. In non-central collisions we predict the existence of “streams” of excited matter moving very close to the spectator system in configuration (x, y, z) space. This picture is consistent with our earlier findings on the longitudinal evolution of the system as deduced from electromagnetic effects on charged pion directed flow and charged pion ratios.

Electromagnetic effects on meson production: a new tool for studying the space-time evolution of heavy ion collisions

We review our studies of spectator-induced electromagnetic (EM) effects on the emission of charged mesons in the final state of ultrarelativistic heavy ion collisions. We argue that these effects offer sensitivity to the distance dE between the charged meson formation zone at freeze-out and the spectator system. As such, they can serve as an independent, new tool to probe the space-time and longitudinal evolution of the system created in the collision. As a phenomenological application for this tool in the context of resonance production and decay, we obtain a first estimate of the time of pion emission from EM effects. This we compare to existing HBT data.