Longitudinal development of air-shower electrons studied from the arrival time distributions of atmospheric Cerenkov light measured at 900 m above sea level

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Abstract
The longitudinal development of electrons in extensive air showers around and after the maximum has been studied by measuring the arrival time distributions of atmospheric Cerenkov light from air showers, with primary energies in the range 5*1015 to 2*1017 eV, in the Akeno air-shower array. These arrival time distributions are consistent with those calculated for slow shower development, as would be expected from a model with low multiplicity of particle interactions, as well as for very fast development before the maximum expected from a model with very high multiplicity combined with slow development after the maximum. This implies that the arrival time distributions measured at a low altitude in practice do not lead to a unique solution to the question of the longitudinal development of the shower through the atmosphere. The variation of the mean depth of the maximum development with electron size has also been determined from the arrival time distributions. The comparison with depths calculated from various models of particle interactions suggests the absence of any appreciable changes in the nuclear composition of primary cosmic rays and the character of particle interactions between 5*1015 and 2*1017 eV.