No-thinning simulations of extensive air showers and small scale fluctuations at the ground level

The particle density in extensive air showers fluctuates at the ground level. These fluctuations, at the scale of the scintillator detector size (several meters), lead to the diversity of the individual detector responses. Therefore, small scale fluctuations contribute to the error in the estimation of the primary energy by a ground array. This contribution is shown to be non-Gaussian. The impact on the primary energy spectrum measured by a ground array is estimated. It is argued that super-GZK events observed by AGASA experiment do not result from the energy overestimation, due to small scale fluctuations, of lower energy events.