30TH INTERNATIONAL COSMIC RAY CONFERENCE Lateral distribution and the energy determination of showers along the ankle

The normalization constant of the lateral distribution function (LDF) of an extensive air shower is a monotonous (almost linear) increasing function of the energy of the primary. Therefore, the interpolated signal at some fixed distance from the core can be calibrated to estimate the energy of the shower. There is, somehow surprisingly, a reconstructed optimal distance, ropt, at which the effects on the inferred signal, S(ropt), of the uncertainties on true core location, LDF functional form and shower-to-shower fluctuations are minimized. We calculate the value of ropt as a function of surface detector separation, energy and zenith angle and we demonstrate the advantage of using the ropt value of each individual shower instead of a same fixed distance for every shower, specially in dealing with events with saturated stations. The effects on the determined spectrum are also shown.