Results from the Pierre Auger Observatory

Abstract. The Pierre Auger Observatory has been designed to investigate the origin and the nature of Ultra High Energy Cosmic Rays using a hybrid detection technique. It is located in the Province of Mendoza, Argentina, and consists of a surface array of about 3000 km2 overlooked by 27 air fluorescence telescopes grouped in four sites, which together provide a powerful instrument for air shower reconstruction. The combination of information from the surface array, measuring the lateral distributions of secondary particles at the ground, and the fluorescence telescopes, observing the longitudinal profile, enhances the reconstruction capability with respect to the individual detector components. Ultra High Energy Cosmic Rays offer also the unique chance of investigating particle interactions over an energy range well beyond the one covered by present and future ground-based particle accelerators. A review of selected results is presented with the emphasis given to the measurement of energy spectrum, arrival directions, chemical composition and the search for photons and neutrinos as primary particles.