Pierre Auger Observatory
Ultra-High Energy Cosmic Rays with the Pierre Auger Observatory: The highest energy cosmic ray ever measured had an energy of 3x1020 eV. It is still a big mystery where these particles come from and how they acquire their energies. It is difficult to imagine that known celestial objects can accelerate ordinary particles to such energies. As these particles will quickly loose their energy on their travel through space, their origin must be rather close to Earth. The highest energy events seem to originate from locations at the sky correlated to the matter distribution in the nearby universe. The flux of the highest energy cosmic rays is less than 1 particle per km2 and century. Therefore huge detectors are needed to measure a sufficient number of events during the finite lifetime of an experiment. The Pierre Auger Observatory is about to solve some of the mysteries around their origin. It consists of a 3000 km2 cosmic ray detector in Argentina which is taking data since 2004.
Results on the energy spectrum, the arrival directions and the mass composition have been published here.
Past experiments with much smaller aperture are: Telescope Array, Hires, AGASA, Haverah Park. A planned space experiment is EUSO.
Info on Leeds Auger group
