Data on multiplicities of charged particles produced in proton-nucleus and nucleus-nucleus collisions at 200 GeV per nucleon are presented. It is shown that the mean multiplicity of negative particles is proportional to the mean number of nucleons participating in the collision both for nucleus-nucleus and proton-nucleus collisions. The apparent consistency of pion multiplicity data with the assumption of an incoherent superposition of nucleon-nucleon collisions is critically discussed.
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From an exposure of the Argonne National Laboratory 12-foot bubble chamber to a beam of 12.4-GeV/c protons we have obtained a 3649-event sample of the reaction pp→γ+anything, where we observe photon conversions into e+e− pairs in the liquid hydrogen. We find that the invariant cross section for this reaction does not separate in its x and P⊥ dependence at our energy. By setting upper bounds on the cross sections for inclusive η and Σ0 production, we show that π0 decay is the dominant source of photons and therefore measure the cross section for inclusive π0 production to be σ(π0)=(31.5±2.6) mb. Comparison with the inclusive π+ and π− cross sections at 12.0 GeV/c shows that the relation 2σ(π0)=σ(π+)+σ(π−) is well satisfied. We confirm earlier indications that the average number of π0's per inelastic pp interaction is approximately independent of the number of associated charged particles produced.
Axis error includes +- 8/8 contribution (THE CROSS SECTION FOR NON-PI0 GAMMA PRODUCTION IS LESS THAN 2.3 MB AND HAS BEEN NEGLECTED IN OBTAINING THE 31.5+-2.6 MB CROSS SECTION FOR THE INCLUSIVE PI0 PRODUCTION).
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