Composition studies of Ultra High Energy Cosmic Rays using Data of the Pierre Auger Observatory

The subject of this work is the estimation of the mass composition of Ultra High Energy Cosmic Rays recorded by the surface detector of the Pierre Auger Observatory. The time traces of the surface detector stations are explored to obtain a new observable sensitive to the mass composition. The new observable is calibrated with the most mass-sensitive observable of the Observatory, the depth of the shower maximum to obtain a new estimation. Results on mass composition, from this, are reported.