Astroparticle Physics

The main goal of this thesis is the investigation of the arrival directions of ultra-high energy cosmic rays (UHECRs). The clustering of such events, collected by the Pierre Auger Observatory, is used to infer the nature of sources and their density, as well as other physical unknowns. Results are based on the comparison between real and simulated data. Hence, an ad hoc Monte Carlo code (HERMES) for the realistic simulation of UHECR propagation in the Universe and a novel method (MAF) to quantify the amount of clustering in a data set of few UHECR events have been developed. In the first chapter, a general overview of UHECR physics will be given, with particular attention to the Pierre Auger Observatory and the most recent results regarding its measurements. In the second and third chapters, we will present the general structure of our propagation code and we will discuss all the models, the parameterizations and the procedures adopted to simulate the propagation of UHECRs in a magnetized Universe. In the second chapter, magnetic fields are treated, and their impact on the propagation of UHECRs is discussed. In particular, we will simulate the diffusion of charged particles in both turbulent and structured magnetic fields for energy values ranging from 1017 eV to 1021 eV. In the third chapter, the propagation of protons, heavier nuclei, photons an