Samenvatting

The Pierre Auger group is studying ultra-high energy cosmic rays. Cosmic rays are charged particles which permanently hit and penetrate the atmosphere of the Earth. They will at a certain moment collide with nuclei in the atmosphere, like nitrogen. The results of such an interaction are new particles, which are called secondary particles. Every secondary particle will decay or interact again with the atmosphere. This process results in a cascade of particles, which is called an extensive air shower. At a given moment the shower becomes less dense, because the average particle energy is not enough to create more particles. The depth where the number of charged particles is on its maximum is called the shower max.

The cosmic rays are detected with surface detectors and fluorescence detectors. The surface detector detects the particles which reach the ground, using large tank filled with water. The Cherenkov radiation, which is emitted by particles that move faster than speed of light in water, is detected by photomultipliers. The fluorescence detector detects the ultraviolet light of the molecules in the atmosphere that fall back to the ground state after being excited by a secondary particle.

The Auger Collaboration reconstructs the data measured by these detectors and analyzes them. There are two reconstruction packages: Offline and CDAS, which contains different output parameters. The differences are mainly due to a different calibration and different corrections for some measurements. Also the algorithm itself is different.

For the research to the nature of the cosmic rays, the mass of the primary particle has to be known. This can be calculated from the fluorescence detectors using the shower max. But these detectors only have a duty cycle of about 10% due to moon and day light as well as the weather conditions. The surface detectors have a duty cycle of 100%. To get enough data to perform composition research at high energies, a parameter reconstructed from the information obtained from the surface detectors which is mass sensitive is needed. This parameter is the radius of curvature of the shower front. Using good quality reconstructed showers and a correction for the angle at which the shower penetrates the Earth, the radius of curvature correlates with the depth of the shower maximum and is therefore mass sensitive.