The Ratio of Soft and Hard Particles in Air Showers

Abstract

While the density spectrum of air showers is well established for energies above ${10}^{13}$ ev, doubt has recently been cast upon the customary procedure of identifying the energy spectrum of the shower-initiating particles calculated from this density distribution with the primary cosmic-ray spectrum. These two distributions would differ if the mechanism of energy transfer to the electron component itself varied with energy. As a result, one would then expect to find a variation with energy also in the amount and composition of the penetrating component of extensive showers. Previous investigations of penetrating particles in air showers do not extend below ${10}^{13}$ ev because of the bias imposed, in the case of low density showers, by the addition of a shielded tray. An experiment was therefore carried out at Mt. Evans, Colorado, altitude 4300 m, and at Echo Lake, Colorado, altitude 3260 m, in order to compare the penetrating components of showers in the ${10}^{13}$-ev region and in the ${10}^{14}$-ev region at a similar stage of their cascade development. The relative abundance of penetrating particles was (2.06±0.11)×${10}^{-2\mathrm{}}$ at Mt. Evans, and (1.20±0.11)×${10}^{-2\mathrm{}}$ at Echo Lake, and the fraction of $N$-particles among the penetrating component was (62±7) percent for the lower, and (38±6) percent for the higher shower energies. The ratio of $\mu$-mesons to electrons was the same for both energy ranges. The results are therefore consistent with the assumption that the development of the large mixed cascades in air is based on the same processes for all energies above ${10}^{13}$ ev, demanding only a slight increase in the multiplicity of meson production with increasing primary energy.