Highptpions as probes of the dense phase of relativistic heavy ion collisions

The properties of pions from the hot and dense reaction stage of relativistic heavy ion collisions are investigated with the Quantum Molecular Dynamics model. Pions originating from this reaction stage stem from resonance decay with enhanced mass. They carry high transverse moments. The calculation shows a direct correlation between high ${\mathit{p}}_{\mathit{t}}$ pions, early freeze-out times, and high freeze-out densities. A measurement of the mass distributions of p-π correlations (e.g., the ${\mathrm{\Delta }}^{++}$) in different ${\mathit{p}}_{\mathit{t}}$ bins is proposed to distinguish different reaction stages.