The AUGER project

Experiment Home Page: http://www.auger.org/

The Pierre Auger Observatory is an international scientific project with the objective of studying the highest energy cosmic rays.

Cosmic rays of energy of the order of 10^20 eV have been observed. The origin and accelerating process of these particles is still unknown. Their rate is extremely low. One expects approximately one cosmic ray arriving on an area of one km2 per century.

In order to collect a significant statistics, the Pierre Auger Observatory covers an area of 3000 km2. The cosmic rays properties are measured by two independent detector systems. The Surface Detector is a giant array of 1600 water Cherenkov tanks, placed over the area with 1.5 km spacing.

The Fluorescence Detector is a telescope system which reconstructs the cosmic ray shower from the fluorescence light emitted by the atmospheric nitrogen excited by the particles of the cosmic ray shower.

Surface arrays measure the lateral distribution of particles in air showers when theystrike the ground. Fluorescence detectors view the longitudinal development of showers as they move downward through the atmosphere. These two complementary techniques form a uniquely powerful instrument to study the nature of extreme energy cosmic rays.

The Southern Obsevatory will be built in Malargue (Argentina). It is expected to measure the arrival direction, the energy and mass composition of primary cosmic rays collecting about 60 events per year with energy above 1020 eV and 6000 events per year above 1019 eV.

An "Engineering Array" with 40 tanks and two fluorescence detector telescopes will be installed at the beginning of the year 2001. It will gradually expand into the full Observatory.

The basic motivations for the AUGER Observatory can be listed as follows:

1. Protons in the cosmic radiation exist with energies above 1020 eV. The most energetic observed until now has an energy of 3x1020 eV (50 joules). More than 20 events with energy above 1020 eV have been already observed.
2. There is no understanding how known astrophysical objects can accelerate protons to energies above 1020 eV.
3. There is mounting evidence that some of these protons come from point sources.
4. Because of interaction with the 2.7 K cosmic background radiation the sources must be close on a cosmological scale (distance less than 50 Mpc or 150 million light years).
5. These protons are little affected by the magnetic field of our galaxy or the extra-galactic magnetic field. Their arrival direction should point to their source giving a new form of astronomy.
6. The prospect for the discovery of new physics or astrophysics is likely.