Ultra high energy cosmic rays

Abstract

Ultra High Energy Cosmic Rays (UHECRs) represent the most energetic source of elementary particles available to scientists. They have macroscopic energies, exceeding 5 × 1019 eV, and as yet unidentified sources. Unfortunately, their flux is as low as one particle per century per square kilometre, requiring dedicated detectors with huge apertures to obtain high-quality and statistically significant data-sets. Over the last three to four decades, a few tens of events at extreme energies were detected by ground-based cosmic ray detectors, opening a new window in the field of astroparticle physics. In this article, the physics of cosmic rays is reviewed briefly. We present a short history and the present status of the field mainly from an experimental point of view. Special attention is given to the Pierre Auger Observatory, the world's largest operating hybrid detector. The most recent and fascinating results are also presented and discussed. Finally, some attention is given to the next generation of detectors devoted to the exploration of the highest energy ranges, which is likely to dramatically increase our knowledge about UHECRs in the near future.