Production of neutral pions in heavy-ion collisions at E/sub lab//A = 25 MeV

Inclusive production of neutral pions was observed at E/sub lab//A = 25 MeV in the reactions 16O+Al,Ni→π0+X. Neutral pions were detected by observing their two decay γ rays in coincidence in an array of 20 Pb-glass Cerenkov-detector telescopes. An array of plastic Cerenkov detectors was added to the above array to tag and reject a significant cosmic-ray background. The observed cross sections are much larger than predicted by nucleon-nucleon collision or statistical models, even if cooperative action of target and projectile nucleons and cluster formation in the final channel are taken into account. This indicates the presence of a collective production mechanism