The Role of Mobile Phones in Tanzania’s Informal Construction Sector:The Case of Dar es Salaam

The Pierre Auger Observatory is currently the largest detector for measurements of cosmic rays with energies beyond 10^18 eV. It uses a hybrid detection method with fluorescence telescopes and surface detector stations. Cosmic rays with energies above 10^15 eV cannot be studied directly but they interact with the atmosphere and produce secondary particle cascades, called extensive air shower. These air showers carry information about the energy, the arrival direction and the chemical composition of the primary cosmic ray particle. The fluorescence telescopes measure the longitudinal air shower profile, whereas the surface detector stations study the lateral profile on the ground. The combination of both detectors provides measurements of cosmic rays with high accuracy.This thesis is focused on the study of the chemical composition of cosmic rays with the virtual fluorescence telescope HECO, which is the combination of the low energy enhancement HEAT (High Elevation Auger Telescopes) and the Coihueco telescope station. HEAT consists of 3 additional fluorescence telescopes, extending the energy range down to below 10^17.0 eV. The cosmic rays with energies between 10^17 eV to 10^18.4 eV are studied, which is the expected transition region from galactic to extra galactic cosmic rays.For the analysis of the chemical composition the atmospheric depth of the air shower maximum Xmax is used. The distribution of Xmax is depending on the atomic mass of the primary cosmic ray particle.An improved profile reconstruction using air shower universality is introduced in the reconstruction and several cross checks on the acquired data and simulations are performed. A complete Monte Carlo based composition analysis is performed to validate the analysis method. The systematic uncertainties of the analysis are studied in detail. The resulting first moments, the mean and the variance of the measured Xmax-distribution per energy bin are compared to theoretical predictions from current cosmic ray interaction models. Additionally, a new fit method is introduced to fit chemical composition fractions based on prediction from interaction models. A parametrization based on Gumbel statistics and air shower simulation is used to describe the Xmax-distribution as a function of energy and primary atomic mass. A superposition model of these parametrization is fitted on a simulated scenario to find the optimal fit routine. The method is applied on the measured Xmax data including all know systematic uncertainties. The findings of this thesis are compared to published results of other experiments. The results of all interaction models suggest a heavy composition at 10^17.0 eV that becomes lighter up to 10^18.4 eV, where it is composed of a mixture of nuclei with light atomic masses