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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.