Recent results from the Pierre Auger Observatory

Abstract

The goal of the Pierre Auger Observatory is to determine the still unknown nature and origin of ultra-high energy cosmic rays. The study of these elusive particles probes astrophysical sites of particle acceleration as well as fundamental interactions at energies unattainable in accelerator facilities. Auger combines two observational techniques, a large surface array and air fluorescence detectors, to observe the extended air showers generated in the atmosphere by cosmic rays. This hybrid observation yields an excellent resolution and allows for important cross-checks. The Auger South site, located in Mendoza (Argentina), is now nearing completion, with 60% of its surface array and three out of its four fluorescence detectors in operation. First results on the energy spectrum measurement, the search for anisotropies in arrival directions and the upper limit on the photon fraction are discussed.