A Study of the Coarse Chemical Composition of Cosmic Radiation between 300 and 1000 Tev Et Al. (hegra Collaboration) 2

An analysis of the chemical composition between 300 and 1000 TeV based on the uctuation of the shower maximum using data from the AIROBICC and scintillator array of the HEGRA installation is presented. Within the errors the composition is in agreement with the low energy composition over the whole energy range. The chemical composition beyond about 100 TeV will provide a decisive clue about cosmic-ray origin because nearly all current theories predict large changes in the composition which rising energy. Direct measurements in balloon and satellites are di cult in this energy range because of the small primary ux. A major e ort is therefore underway at many places[1] to develop a methology to reliably derive the chemical composition from data gathered with ground based installations with their very large collecting areas. Here we present a method based on the measurement of the lateral distribution atmospheric Cerenkov light and the electron number N e and apply it to a small subsample of the data collected with the AIROBICC[2] and scintillator array of the HEGRA installation[3] at La Palma. The analysis extends over an energy range with just overlaps with the last datapoint from a large balloon experiment[4]. The basic idea of our analysis is to derive the chemical composition from the uctuations of the height of the shower maximum. It is well known [1] that proton induced showers have a uctuation which is about a factor of 3 larger than that of iron induced showers. This is a large factor and one would think it should be easy to discriminate these two components. Moreover, especially for high energies, the size of the uctuation is determined 1 present address: IfH DESY-Zeuthen,D-15735 Zeuthen, Germany 2 for complete author list see contribution by V.Fonseca et al.