Nuclear interactions and primary cosmic-ray component around1015eV viewed through the cluster analysis ofγ-ray families

Abstract

An analysis of the $\gamma$-ray families ($\Sigma E_{\gamma }\gtrsim 100$ TeV) obtained with the Mt. Fuji emulsion chambers was made focusing attention on the cluster structure of families, and the validity of scaling in the fragmentation region in the ${10}^{15}$-eV region was examined by comparing the results with those of artificial families. We deduced that (i) scaling in the fragmentation region (Feynman $x>\mathrm{}0.1\mathrm{}$) is not broken appreciably, at least below ${10}^{15}$ eV, (ii) scaling in the central region ($x<<0.1\mathrm{}$) seems to be broken largely at $E>\mathrm{}{10}^{15}$ eV; multiplicity increases proportionally to $E^{\frac{1}{4}}$ or even stronger (say, $\propto E^{\frac{1}{3}}$), (iii) the iron component in the primary cosmic rays rapidly increases and occupies 60-70% of the total flux at ${10}^{15}$ eV and that of the protons decreases to ≃ 10%, and (iv) the average transverse momentum of produced pions in the fragmentation region stays within ∼400 MeV/c.