The origin of the hump in the Cerenkov lateral distribution in gamma-ray showers and a possible means of separating them from proton showers

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Abstract
The lateral distribution of Cerenkov photons emitted by 100 GeV electromagnetic cascades is calculated using a detailed Monte Carlo procedure. The calculated lateral distribution shows a prominent hump at a distance of about 135 m from the core. The nature and origin of this hump are investigated analytically as well as through Monte Carlo calculations and it is shown to be due to electrons of energy >1 GeV, above which the root mean square scattering angle is less than the Cerenkov emission angle. The conditions under which such a hump can arise are derived. Arguments are given to show that such a hump is not present in proton showers of comparable energy. Possible implications for identification of gamma rays against the cosmic-ray background are discussed.