Bellido Caceres, Jose AlfredoDawson, Bruce RobertBlaess, Simon Garry2018-06-212018-06-212018http://hdl.handle.net/2440/112998Knowledge of the acceleration mechanisms, possible sources and arrival direction distribution of ultra high energy cosmic rays can be furthered by increasing our understanding of the cosmic ray mass composition. The Pierre Auger Observatory measures the depth of shower maximum (Xmax [max subscript]) of ultra high energy cosmic rays, an observable which is sensitive to the mass of the cosmic ray, and often analysed in mass composition studies. At ultra high energies, the results of mass composition studies depend strongly on the particle interaction predictions of the assumed hadronic interaction model. A novel approach to reduce the model dependency in the interpretation of the mass composition will be outlined in this thesis. The Xmax [max subscript] predictions of the models were parameterised in terms of the primary mass. The mass composition fractions and some of the parameterisation coefficients are then fitted to the data, resulting in a mass composition estimate which is of reduced model dependency. The results of this approach applied to Pierre Auger Observatory data are presented.Cosmic raysmasscompositionXmaxPierre Auger ObservatoryTheses