Inclusive production of neutral pions was observed at $E_{\mathrm{lab}/\mathrm{A}=25\mathrm{}}$ MeV in the reactions ${}_{}{}^{16}{}_{}{}^{}$O+Al,Ni→${\pi }^0$+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.

• Received 23 September 1985

DOI:https://doi.org/10.1103/PhysRevC.33.742