Response of a water-Cherenkov detector to inclined muons at the Pierre Auger Observatory ; Resposta de um tanque de Cherenkov do Observatório Pierre Auger a muões inclinados

Dissertação de mestrado em Física Aplicada ; Recent studies performed to highly inclined (with zenith angle larger than 60°), hybrid events collected by the Pierre Auger Collaboration show disagreements between data and simulations, with a deficit on the muon content between 30% and 80%, depending on the hadronic interaction model used. However, large uncertainties (11%) were still associated with the muon measurements at inclined angles. Following the need to have an accurate study of the response of the water Cherenkov detectors (WCD) to inclined muons, a new experimental campaign with the RCP hodoscope at the Gianni Navarra test tank took place. The data acquisition was monitored and analysed in detail, allowing to study the behaviour of the RPCs in these conditions. A sample of muons with a zenith angle distribution between [62; 68]° was collected and studied. Unaccounted background sources (possibly electrons and small showers) were found in the data, that made the analysis of the response of theWCDcomplex. Nonetheless, the charge peak variation with the reconstructed track length is compatible between data and simulation, in the premise that the former is rescaled to take into account the bias introduced by the background contaminations. Additionally, direct light effects to one PMT were also studied and some discrepancies were found. These differences were discussed in the context of the ageing effects and of the background found in the data. ; Estudos recentes feitos com eventos híbridos e bastante inclinados (com ângulo zenital maior que 60°), colectados pela Colaboração Pierre Auger mostram desacordos entre dados e simulações, com um défice no número de muões entre 30% e 80%, dependendo do modelo de interacção hadrónica utilizado. Contudo, incertezas elevadas (11%) permanecem associadas às medidas de muões inclinados. Seguindo a necessidade de estudar com precisão a resposta do tanque de Cherenkov a muões inclinados, foi iniciada uma nova aquisição de dados com o hodoscópio de RPCs colocado sobre o ...