Longitudinal development of air-shower electrons studied from the arrival time distributions of atmospheric Cerenkov light measured at 5200 m above sea level

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Abstract
The longitudinal development of electrons in extensive air showers before the maximum has been studied by measuring the arrival time distributions of atmospheric Cerenkov light from air showers, with primary energies in the range 6*1015 to 2*1017 eV, in the Chacaltaya air-shower array. The Cerenkov light apparatus was the same as that operated at the Akeno air-shower array. These arrival time distributions are consistent with those calculated using a model of particle interactions which contains Feynman scaling in the fragmentation region, an E1/2 multiplicity law in the pionisation region and a rising cross section for primary protons. Such a model also reproduces the arrival time distributions of Cerenkov light measured in the Akeno air-shower array which implies a very fast development before the maximum and a slow development after the maximum. The multiplicity in this model is much higher than that given by an extrapolation of empirical formulae for multiplicities measured with accelerators up to s1/2 of 540 GeV and therefore the present result suggests a commencement of particle interactions with copious production of pi +or- and pi 0 or gamma rays above 1016 eV.