On the possibility of primary identification of individual cosmic ray   showers
  The transition between the Galactic and extragalactic cosmic ray components could take place either in the region of the spectrum known as the second knee or in the ankle. There are several models of the transition but it is not possible to confirm or even rule out any of them from the flux measurement alone. Therefore, the measurement of the composition as a function of primary energy will play a fundamental role for the understanding of this phenomenon.   In this work we study the possibility of primary identification in an event by event basis in the ankle region, around $E = 10^{18}$ eV. We consider as case study the enhancements of the Pierre Auger Southern Observatory, which are under construction in Malague, Province of Mendoza, Argentina. We use a non-parametric technique to estimate the density functions, from Monte Carlo data, corresponding to different combination of mass sensitive parameters and type of primaries. These estimates are used to obtain the classification probability of protons and iron nuclei for the different combination of parameters considered. We find that, after considering all relevant fluctuations, the maximum classification probability obtained combining surface and fluorescence detectors parameters is of order of 90%. 
A. D. Supanitsky, G. Medina-Tanco, A. Etchegoyen