2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/82912Medium Effects in low-mass dilepton production in ultra-relativistic heavy-ion collisions are investigated using hadronic models. The rescattering of pions and rho mesons within a hot and dense hadron gas leads to substantial modifications in the $π^+π^- \to e^+ e^-$ annihilation process, which are shown to be important for understanding the recently observed dilepton enhancement at the CERN-SpS. Possible implications for the nature of the chiral phase transition are outlined.Proceedings of 33rd Recontres de Moriond, Les Arcs, France, March 23-27 1998; 6 pages LaTeX, 3ps-/eps-figures, including moriond.styNuclear Theorytext