Gamma production in p 20Ne and pN interactions at 300 GeV.

Abstract

Data on the multiplicity and inclusive spectra of $\ensuremath{\gamma}$ produced in inelastic $p^{20}\mathrm{Ne}$ and $\mathrm{pN}$ interactions at 300 GeV are presented. The $\ensuremath{\gamma}$ multiplicity for $p^{20}\mathrm{Ne}$ interactions is 11.43\ifmmode\pm\else\textpm\fi{}0.23, and the ratio of $〈{n}_{\ensuremath{\gamma}}〉$ for $p^{20}\mathrm{Ne}$ and $\mathrm{pN}$ interactions is 1.48\ifmmode\pm\else\textpm\fi{}0.05. From an analysis of the effective-mass distributions, $〈{n}_{{\ensuremath{\pi}}^{0}}〉=4.91\ifmmode\pm\else\textpm\fi{}0.52$ and $〈{n}_{{\ensuremath{\eta}}^{0}}〉=1.47\ifmmode\pm\else\textpm\fi{}0.33$. In fact, ${\ensuremath{\eta}}^{0}$ production is much higher in $p^{20}\mathrm{Ne}$ interactions [$R(\frac{{\ensuremath{\eta}}^{0}}{{\ensuremath{\pi}}^{0}})=0.66\ifmmode\pm\else\textpm\fi{}0.12$ for ${n}_{p}\ensuremath{\ge}21$] than in $\mathrm{pN}$ interactions [$R(\frac{{\ensuremath{\eta}}^{0}}{{\ensuremath{\pi}}^{0}})=0.06\ifmmode\pm\else\textpm\fi{}0.04$]. No ${\ensuremath{\eta}}^{\ensuremath{'}}(958)$ signal is seen. Strong correlations between $〈{n}_{\ensuremath{\gamma}}〉$ and ${n}_{p}$, the number of secondary protons, are observed, primarily from the central and target fragmentation regions. Inclusive ${y}^{*}$ and ${p}_{\ensuremath{\perp}}$ spectra are analyzed and evidence for low-energy cascading and rescattering of fast particles in the projectile fragmentation region is discussed. The data are compared to the predictions of the additive quark model, the Lund model, and the dual parton model.