The age parameter of ultrahigh-energy cosmic γ-ray showers

Abstract

The lateral-age parameter of EAS as a possible parameter for distinguishing between photonic- and nucleonic-initiated showers is investigated by Monte Carlo simulation. Contrary to what has been assumed by many workers in the past, we find that γ-ray-initiated showers tend to be younger at most observing levels, with the difference being outside experimental resolution at sea level. This makes difficult to understand some reported directional excesses of ultrahigh-energy cosmic-rays as arising from primary γ-rays.