Study of Inclusive γ and π 0 Production in 12.4-GeV/ c pp Interactions

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 $\mathrm{pp}\ensuremath{\rightarrow}\ensuremath{\gamma}+\mathrm{anything}$, where we observe photon conversions into ${e}^{+}{e}^{\ensuremath{-}}$ pairs in the liquid hydrogen. We find that the invariant cross section for this reaction does not separate in its $x$ and ${P}_{\ensuremath{\perp}}$ dependence at our energy. By setting upper bounds on the cross sections for inclusive $\ensuremath{\eta}$ and ${\ensuremath{\Sigma}}^{0}$ production, we show that ${\ensuremath{\pi}}^{0}$ decay is the dominant source of photons and therefore measure the cross section for inclusive ${\ensuremath{\pi}}^{0}$ production to be $\ensuremath{\sigma}({\ensuremath{\pi}}^{0})=(31.5\ifmmode\pm\else\textpm\fi{}2.6)$ mb. Comparison with the inclusive ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\ensuremath{-}}$ cross sections at 12.0 GeV/c shows that the relation $2\ensuremath{\sigma}({\ensuremath{\pi}}^{0})=\ensuremath{\sigma}({\ensuremath{\pi}}^{+})+\ensuremath{\sigma}({\ensuremath{\pi}}^{\ensuremath{-}})$ is well satisfied. We confirm earlier indications that the average number of ${\ensuremath{\pi}}^{0}'\mathrm{s}$ per inelastic $\mathrm{pp}$ interaction is approximately independent of the number of associated charged particles produced.