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We report a measurement of the energy spectrum of cosmic rays for energies above 2.5×1018 eV based on 215,030 events recorded with zenith angles below 60°. A key feature of the work is that the estimates of the energies are independent of assumptions about the unknown hadronic physics or of the primary mass composition. The measurement is the most precise made hitherto with the accumulated exposure being so large that the measurements of the flux are dominated by systematic uncertainties except at energies above 5×1019 eV. The principal conclusions are(1) The flattening of the spectrum near 5×1018 eV, the so-called "ankle,"is confirmed.(2) The steepening of the spectrum at around 5×1019 eV is confirmed.(3) A new feature has been identified in the spectrum: in the region above the ankle the spectral index γ of the particle flux (∝E-γ) changes from 2.51±0.03 (stat)±0.05 (syst) to 3.05±0.05 (stat)±0.10 (syst) before changing sharply to 5.1±0.3 (stat)±0.1 (syst) above 5×1019 eV.(4) No evidence for any dependence of the spectrum on declination has been found other than a mild excess from the Southern Hemisphere that is consistent with the anisotropy observed above 8×1018 eV.

In this paper we study the depth at which a cosmic ray shower reaches its maximum (\Xmax) as predicted by Monte Carlo simulation. The use of \Xmax in the determination of the primary particle mass can only be done by comparing the measured values with simulation predictions. For this reason it is important to study the differences between the available simulation models. We have done a study of the first and second moments of the \Xmax distribution using the \Corsika and \Conex programs. The study was done with high statistics in the energy range from $10^{17}$ to \energy{20.4}. We focus our analysis in the different implementations of the hadronic interaction models \Sibyll and \Qgsjet in \Corsika and \Conex. We show that the predictions of the \meanXmax and \sigmaXmax depend slightly on the combination of simulation program and hadronic interaction model. Although these differences are small, they are not negligible in some cases (up to 5 g/cm$^2$ for the worse case) and they should be considered as a systematic uncertainty of the model predictions for \meanXmax and \sigmaXmax. We have included a table with the suggested systematic uncertainties for the model predictions. Finally, we present a parametrization of the \Xmax distribution as a function of mass and energy according to the models \Sibyll and \Qgsjet, and showed an example of its application to obtain the predicted \Xmax distributions from cosmic ray propagation models., Submitted to Astroparticle Physics

The production of energetic particles in the universe remains one of the great mysteries of modern science. The mechanisms of acceleration in astrophysical sources and the details about the propagation through the galactic and extragalactic media are still to be defined. In recent years, the cosmic ray flux has been measured with high precision in the energy range from \energy{10} to \energyEV{20.5} by several experiments using different techniques. In some energy ranges, it has been possible to determine the flux of individual elements (hydrogen to iron nuclei). This paper explores an astrophysical scenario in which only our Galaxy and the radio galaxy Cen A produce all particles measured on Earth in the energy range from \energy{10} to \energyEV{20.5}. Data from AMS-02, CREAM, KASCADE, KASCADE-Grande and the Pierre Auger Observatories are considered. The model developed here is able to describe the total and individual particle flux of all experiments considered. It is shown that the theory used here is able to describe the smooth transition from space-based to ground-based measurements. The flux of each element as determined by KASCADE and KASCADE-Grande and the mass sensitivity parameter \xmax measured by the Pierre Auger Observatory above \energyEV{18} are also explored within the framework of the model. The transition from \energy{16} to \energyEV{18} is carefully analyzed. It is shown that the data measured in this energy range suggest the existence of an extra component of cosmic rays yet to be understood.

In this dissertation we provide new benchmark scenarios for galactic cosmic ray propagation in view of the recent precise measurements of the Boron to Carbon flux ratio from the Alpha Magnetic Spectrometer (AMS-02), based on fits to data using the USINE code. We identify a general scenario that provides excellent fits to the data and includes all relevant physical processes, the BIG model. This model has two limiting regimes: the SLIM model, which is characterised by a minimal diffusion-only description, as well as the QUAINT model, with reacceleration and convection. Moreover, we present a study of the spectral index of the B/C ratio, aiming at understanding the differences between this observable and the diffusion coefficient spectral index, showing that these two quantities are not interchangeable. We generalize our analysis to all CR nuclei, from H to Fe, and compare to existing AMS-02 measurements. Nesta dissertação nós apresentamos novos cenários de referência para a propagação de raios cósmicos galáticos, tendo em vista medidas precisas feitas recentemente pelo Espectrômetro Magnético Alfa (AMS-02), da razão do fluxo de Boro sobre Carbono (B/C). Os resultados apresentados são baseados em ajustes aos dados usando o código USINE. Identificamos um cenário geral que fornece excelentes ajustes aos dados e inclui todos os processos físicos relevantes para a propagação de raios cósmicos, o chamado modelo BIG. Este modelo possui dois casos especiais: o modelo SLIM, que é caracterizado por uma descrição simplificada com apenas difusão, bem como o modelo chamado QUAINT, com reaceleração e convecção. Os três modelos fornecem um excelente ajuste aos dados. Além disso, apresentamos um estudo do índice espectral da razão B/C, visando compreender as diferenças entre o índice espectral desta grandeza e o índice espectral do coeficiente de difusão, mostrando que essas duas grandezas não são equivalentes. Nós generalizamos nossa análise para todos os núcleos de raios cósmicos, de H até Fe, e comparamos com as medidas existentes.

Os detectores de superfície do observatório Pierre Auger são tanques repletos de água e completamente escuros com sensores fotomultiplicadores instalados na parte interna. Quando as partículas carregadas de chuveiros atmosféricos atravessam a água com velocidade acima a da luz nesse meio, geram radiação ultravioleta devido ao efeito Cherenkov. Os sensores fotomultiplicadores desses detectores medem e convertem essa radiação em sinais elétricos que são enviados para a central de dados, registrando assim um evento. Alguns eventos apresentam comportamento incomum, caracterizado por apresentar mais de uma estrutura na série temporal, coincidentes em pelo menos dois detectores de superfície distantes. Esse trabalho se dedicou a investigar sobre as características e origens desses eventos. Devido ao grande número de dados registrados pelo Observatório Pierre Auger, foi preciso desenvolver uma ferramenta computacional para reconhecer e selecionar aqueles eventos que apresentam as estruturas desejadas de forma automática. Após, esse filtro, tentamos determinar um padrão buscando semelhanças ou tendências em variáveis dos chuveiros, como a energia e a direção de chegada. Em segunda análise olhamos para os eventos híbridos, chuveiros observados pelos detectores de superfície e pelos telescópios de fluorescência simultaneamente, de modo a analisar o desenvolvimento longitudinal do chuveiro. Na sequência, foram realizado algumas simulações de chuveiros para alguns dos eventos selecionados com o algoritmo desenvolvido. Esses eventos foram então reconstituídos, simulando uma detecção pelo observatório, com o intuito de determinar se a origem desse sinal anômalo está relacionada a uma resposta dos detectores. O último passo, foi analisar a razão entre a proporção de eventos selecionados e o número total de eventos observados em função da energia da partícula primária, o que revelou uma relação entre essas duas grandezas. The surface detectors of Pierre Auger observatory are water filled tanks and completely dark with photomultiplier sensors installed indoors. When charged particles of air showers cross the water with velocities above that of light in this medium, ultraviolet radiation is generated due to the Cherenkov effect. The photomultiplier sensors of these detectors measure and convert this radiation into electrical signals that are sent to the data center, thus recording an event. Some events have unusual behavior, characterized by having more than one structure in its time series, coincident in at least two distant surface detectors. This work was dedicated to investigate the characteristics and origins of these events. Due to the large amount of data recorded by the Pierre Auger Observatory it was necessary to develop a computational tool to automatically recognize and select those events that present the desired structure type. After applying this filter, we tried to determine a pattern by looking for similarities or trends in air-shower variables, such as energy and direction of arrival. In a second analysis, we looked at the hybrid events, air showers observed by the surface detectors and the fluorescence telescopes simultaneously, in order to analyze the longitudinal development of air shower. In the sequence, we performed some simulations of air showers for some events selected with the developed algorithm. These events were then reconstituted, simulating a detection by the observatory for the purpose of determinin if the origin of this anomalous signal is related to a response of the detectors. The last step was to analyze the ratio between the proportion of selected events and the total number of events observed as a function of the energy of the primary particle, which revealed a relation between these two quantities.