Physics of Extremely High Energy Cosmic Rays

Over the last third of the century, a few tens of events, detected by ground-based cosmic ray detectors, have opened a new window in the field of high-energy astrophysics. These events have macroscopic energies, unobserved sources, an unknown chemical composition and a production and transport mechanism yet to be explained. With a flux as low as one particle per century per square kilometer, only dedicated detectors with huge apertures can bring in the high-quality and statistically significant data needed to answer those questions. In this article, we review the present status of the field both from an experimental and theoretical point of view. Special attention is given to the next generation of detectors devoted to the thorough exploration of the highest energy rangesComment: 43 pages, 12 figures, submitted to International Journal of Modern Physics

Cosmic Rays above 101410^{14} eV

We briefly review the status of cosmic ray studies between $10^{14}$ eV and the highest observed energies, namely a few times $10^{20}$ eV. Because of the rather low incident fluxes in this energy range, the studies mostly rely on ground based, large aperture detectors reconstructing the cosmic ray's properties through the detection of the air-showers they generate by interacting with the atmosphere. We stress the fact that many issues such as the chemical composition of the cosmic rays, their acceleration mechanisms, the structures displayed in their energy spectrum are mostly open questions which may be answered by the next generation of experiments.Comment: 11 pages, 5 figures, Latex2e, one reference modifie

Histoire d’un projet singulier : l’observatoire Pierre Auger

History of a Singular Project : The Pierre Auger Observatory The Pierre Auger Observatory is a giant cosmic ray detector presently in construction in Argentina. Several hundreds of scientists coming from fifteen countries (half of which from Europe) have been working for more than ten years to the design and construction of this unique detector. The aim of the project is to understand the origin and nature of cosmic rays detected in very small numbers whose energies exceed by a factor of several hundreds of millions those of the particles accelerated by the most performing accelerators ever built by men. The article summarizes the genesis and the scientific stakes of this project in which France, and more specifically the CNRS, played a major role

Foreword

International audienc