Quasiparticle properties of the pion and heavy-ion collisions

The quasiparticle spectrum of the pion in nuclear matter is discussed. It contains the three branches: spin-isospin sound, quasifree pion, and the $\Delta$-hole branch. It is demonstrated how the spin-isospin branch is related to the phenomena of pion condensation and precritical scattering. Experimental consequences are derived. An event-by-event analysis of the $n$-particle momentum distribution allows one to measure the order parameter ${\overrightarrow{k}}_{\pi }$ of the condensate and the amount of pre-equilibrium to equilibrium cross section. The importance of the quasifree pion branch for subthreshold pion production is shown. The inclusive ${\pi }^{\pm }$-production cross section at 0 degrees and a kinetic energy of 34 MeV is calculated for Ne + NaF at 100, 200, and 300 MeV/N.