Study of high energy hadronic cascade through muons
IDPASC Portugal - PHD Programme 2017
2017 / 2018
Theoretical Particle Physics | Astroparticle Physics
Instituto Superior Técnico
Laboratório de Instrumentação e Física Experimental de Partículas
Ultra High Energy Cosmic Rays (UHECR) are the most energetic particles known in nature, being their astrophysical sources and nature still unknown. As they enter the Earth’s atmosphere they collide with atoms generating typically thousands of secondaries, which can interact again, creating a multiplicative process, known as Extensive Air Shower, which can reach up to 10^11 particles at ground level for 10^20 eV showers. The first interactions occur at centre of mass energies up to 400 TeV, more than one order of magnitude above the most energetic man made accelerator. This means that UHECRs are a unique opportunity to study particle physics above the LHC energy scale. However, although the EAS encodes the information about the nature of the primary (which is expected to be of hadronic nature – proton to iron) and about the characteristics of the hadronic interaction (which shapes the development of the EAS), this information is degenerated. A promising tool to break this degeneracy is the study of muons. Muons come from the decays of charged mesons, which are a direct by-product of hadronic interactions. Moreover, muons can travel many kilometers from the hadronic shower almost unaffected, carrying valuable information. The understanding of the muons distributions is an essential key to break the degeneracy between the uncertainties on the extrapolation of the hadronic interaction models to the highest energies and the composition of the UHECR beam. The study of the air shower can be done by means of the cascade equations, assuming some simplifications, or by means of full Monte Carlo simulations that include many important details difficult to account for otherwise. On the other hand, Heitler models offer a simplified version of the main multiplicative process of a cascade and serves to qualitatively understand the most important features, giving approximated values for relevant variables of the cascade. Although Monte Carlo simulations offer the most complete description of the shower, this is done at the cost of losing understanding to the main underlying physics. Hence, in this thesis we propose to investigate the muon distributions of the EAS using analytical models. This is a complex physics problem that requires a combined effort from different points of view: mathematical, statistical and analytical. This would allow not only to identify the main shower properties that drive the muon distributions main characteristics, but also would give a profound knowledge over its connection to the hadronic shower. The results from this work would naturally be used to extract information about the high-energy hadronic interaction from the experimental measurements on the muon distributions, in particular those conducted at the Pierre Auger Observatory.