Measurement of the proton air cross section using hybrid data of the Pierre Auger Observatory

Abstract

The subject of this thesis is the measurement of the proton-air cross section at ultra high energy with hybrid data of the Pierre Auger Observatory. Based on a critical review of the shortcomings of previous air shower measurements, a new analysis method is developed. This analysis method takes into account the most important and relevant experimental and air shower physics effects. The impact of a changed cross section extrapolation on the resulting air shower development is considered in addition to its more obvious effect on the distribution of shower starting points. Furthermore, detector acceptance effects are explicitly included in the reconstruction ansatz, which allows us to use almost the complete data set in the analysis. Systematic uncertainties on the resulting cross sections are thoroughly studied and quantified. Assuming a proton dominated composition, the analysis is applied to hybrid data of the Pierre Auger Observatory. The obtained cross section is, within the statistical and systematic uncertainties, in agreement with predictions from hadronic interaction models up to 10 18.4 eV. At higher energies the resulting cross section increases rapidly. Finally the proton-air cross section is converted to a proton-proton cross section using Glauber theory and limits on the elastic scattering slope are derived.