The lateral distribution of Cerenkov light from extensive air showers

Abstract

Investigations of the cosmic ray flux around the " knee " in the all - particle energy spectrum can provide information on the origin of this steepening. Studies of air shower development in this region are especially informative, although experiments in recent years have produced some conflicting results. Some report an unusually rapid development of showers, which has been interpreted in terms of an increased proportion of heavy nuclei in the flux, compared with the directly measured low energy composition. This thesis describes measurements of the lateral distribution of Cerenkov light associated with air showers with sea level sizes between ~ 10 ^ and 1O7 particles. It is shown that the slope of the lateral distribution is sensitive to air shower development and that the shape is in agreement with the results of recent calculations. These calculations are used to assign depths of maximum to the showers observed. A comprehensive simulation of the selection biases present in the experiment is used in the interpretation of the results on the depth of shower maximum. The data are shown to be consistent with a cosmic ray composition rich in iron in the energy region studied.