Cooperative Effects Observed in theπ0Production from Nucleus-Nucleus Collisions

Cooperative effects in collisions of 60-84-MeV/u ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ projectiles with different target nuclei have been experimentally established through ${\pi }^0$ production, especially through the measurement of the apparent velocity of the pion source. Our method for the spectroscopy of neutral pions covers all angles and kinetic energies (down to zero). The exponential slopes in the spectra contain rather high Fourier components indicating the presence of short-distance phenomena in the collision dynamics.