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Après plus d'un siècle d'études, l'origine des rayons cosmiques d’ultra-haute énergie reste mal comprise. En améliorant la connaissance de la composition des rayons cosmiques détectés sur Terre, il est possible de contraindre les modèles concernant leur origine, ainsi que leur mécanisme de production dans les sources astrophysiques. Les simulations montrent que le champ électrique émis par les gerbes est sensible à leur développement dans l'atmosphère. Ce champ électrique peut être mesuré avec un cycle utile élevé, faisant du signal radio une observable prometteuse pour identifier le rayon cosmique primaire. Le signal radio permet également de mesurer sa direction d'arrivée et son énergie. Depuis 2006, l'observatoire Pierre Auger accueille plusieurs réseaux de radio détection des rayons cosmiques. Des démonstrateurs équipés de quelques stations (RAuger,MAXIMA) ont permis une caractérisation efficace de l'environnement radio du site, ils ont également apporté des contraintes sur les mécanismes responsables de l'émission du champ électrique par les gerbes dans le domaine du MHz. Les prototypes ont mené à la construction d’AERA (Auger Engineering Radio Array) qui, avec 124 stations couvrant 6 km², est le premier réseau grande échelle de radio détection des gerbes dans le domaine du MHz. AERA est déployé dans l'extension basse énergie de l'observatoire afin de bénéficier d'une statistique plus importante. Le réseau permet d'intéressantes mesures hybrides ; son emplacement permet en effet de croiser les données obtenues par la radio avec celles provenant du réseau de surface (SD) et des télescopes à fluorescence (FD) proches du réseau. Cette thèse est dédiée à la caractérisation de signaux transitoires radio détectés par RAuger et AERA. Comme un des défis de la radio détection des gerbes atmosphériques est de supprimer les bruits de fond anthropiques causant des déclenchements accidentels, des méthodes de réjection du bruit de fond et de sélection des coïncidences SD-AERA ont été développées. Une étude de la corrélation entre le développement de la gerbe dans l'atmosphère (profil longitudinal) et le champ électrique mesuré par les stations radio est également présentée. Cette étude valide le lien direct entre le champ électrique et le développement de la gerbe dans l'atmosphère et confirme l’intérêt du signal radio pour l’estimation de la nature des rayons cosmiques d'ultra-haute énergie. / After more than a century of studies, one of the challenging questions related to ultra-high energy cosmic rays concerns their nature, which remains unclear. Improving the knowledge about the composition of cosmic rays will permit to constrain the models concerning their origins and the production mechanisms in the astrophysical sources. Simulations show that, the electric field emitted by the shower is sensitive to its development. This electric-field can be measured with a high duty cycle, and thus is apromising technique to identify an observable sensitive to the nature of the primary cosmic ray. The radio signal is also used to measure its arrival direction and its energy. Since 2006, the Pierre Auger Observatory hosts several radio detection arrays of cosmic rays, starting from small size prototypes (RAuger, MAXIMA) to achieve a large scale array of 124 radio stations: AERA, the Auger Engineering Radio Array covering 6 km². These different arrays allow the study of the radio emission during the development of the shower in the MHz domain. AERA is deployed in the low energy extension of the Pierre Auger Observatory in order to have a larger statistics. It enables interesting hybrid measurements, with the comparison of radio observable with those obtained with the surface detector (SD) and the fluorescence telescopes close to the array. This thesis is dedicated to the characterization of the radio transient signals detected by RAuger and AERA. As one of the challenges of the radio detection of air-shower is to remove the anthropic background causing accidental triggering, methods for background rejection and SD-AERA coincidences selection have been developed. A study of the correlation between the shower development in the atmosphere (longitudinal profile) and the electric-field measured by the radio stations is also presented. This study shows the relationship between the electric-field and the shower development in the atmosphere and confirms that the radio signal is a powerful tool to study the nature of the ultra-high energy cosmic rays.

Les rayons cosmiques sont des particules chargées, ainsi que des coproduits comme les photons et les neutrinos, issus de sources de rayons cosmiques galactiques ou extragalactiques. Ils arrivent au sommet de l'atmosphère terrestre avec des énergies primaires allant jusqu'à quelques 10 EeV. Lorsque les rayons cosmiques entrent dans l'atmosphère, ils interagissent avec les molécules de l'air et produisent un grand nombre de particules secondaires, créant une gerbe atmosphérique (extensive air shower, EAS). Accompagné des particules secondaires, une émission de la lumière Cherenkov et de la lumière fluorescence est induite par le passage des particules dans l'atmosphère. L'Observatoire Pierre Auger et Large High Altitude Air Shower Observatory (LHAASO) sont des observatoires dédiés à la détection des gerbes atmosphériques dans le but de répondre aux questions ouvertes concernant les rayons cosmiques, mais se concentrant sur différentes gammes d'énergie, les plus hautes énergies et les énergies autour de quelques PeV. Après plus de 10 ans d'exploitation de l'Observatoire Pierre Auger, la collaboration Auger a proposé une amélioration des détecteurs de son réseau de surface, appelée "AugerPrime". Le but est d'augmenter la sensibilité à la masse des particules primaires en ajoutant un détecteur scintillateur sur le détecteur Cherenkov à eau. Les deux observatoires sont dits «hybrides» car composés de télescopes optiques observant le développement longitudinal des gerbes et des réseaux de détecteurs de surface échantillonnant leurs profils latéraux. Dans cette thèse, une série d'études contribuant aux projets AugerPrime et LHAASO sont présentées. En ce qui concerne le projet AugerPrime, la présente étude comprend le travail de recherche & développement des scintillateurs et l'analyse de données du réseau de tester. Pour le projet LHAASO, des simulations de télescopes Cherenkov et une analyse multivariée des observations hybrides pour l'identification des masses primaires sont présentées. / Cosmic rays are charged particles, as well as coproducts like photons and neutrinos, originated in cosmic-ray sources inside or outside the Galaxy. They arrive at the top of the Earth's atmosphere with primary energies of up to a few 10 EeV. When the cosmic rays enter the atmosphere, they interact with the molecules in the air and produce a large number of secondary particles, creating an extensive air shower (EAS). The ground-based observation of the EAS can be used to deduce the energy, the arrival direction, and the mass composition of cosmic rays. The Pierre Auger Observatory and the Large High Altitude Air Shower Observatory (LHAASO) are both EAS observatories aiming at solving open questions of cosmic-ray studies but focusing on different energy ranges, the highest-energy and the so-called knee (around few PeV) regions. Based on the experience gained during the operation of the Pierre Auger Observatory for more than 10 years, the Auger collaboration has proposed an upgrade project, called ''AugerPrime'', with the aim of increasing the sensitivity of the surface detector array to the primary mass of cosmic rays. Both observatories employ the so-called ''hybrid detector arrays'' composed of optical telescopes overlooking the longitudinal development and ground detector arrays sampling the signal densities in the lateral direction of the EAS. The ground detector arrays of both observatories are being constructed or upgraded to have various types of particle detectors (scintillator and water-Cherenkov detectors), which allow us to decompose the electromagnetic and muonic components of the EAS. In this thesis, a series of studies contributing to the AugerPrime and LHAASO projects are presented. Concerning the AugerPrime project, the present study includes R&D work of the scintillator detector and data analysis of the engineering array. For the LHAASO project, simulations of the wide field of view Cherenkov telescope array and a multivariate analysis of LHAASO-hybrid observations for the primary mass identification are presented.

O comportamento das interações hadrônicas para energias de centro de massa superiores a 50 TeV/núcleon é uma fonte importante de incerteza sistemática na interpretação de dados de observatórios de raios cósmicos. Nesta tese, estudamos por meio de simulações de Monte Carlo observáveis dos chuveiros atmosféricos que pudessem ser correlacionados com aspectos dos diferentes modelos destas interações. Especial atenção foi dada à componente muônica que sabidamente é gerada do decaimento de partículas de natureza hadrônica na cascata. A precisão e a acurácia de uma rede esparsa de contadores de múons foram estudadas como função da granularidade da rede de detectores e da área de coleção de suas células. Mostramos, em particular, as diferenças na dependência radial da densidade de múons no plano transversal ao eixo da cascata para os diferentes modelos. Tais diferenças se mostram mais acentuadas na vizinhança do eixo e poderiam ser exploradas experimentalmente com um detector com alcance dinâmico suficiente para evitar saturação da eletrônica. Além disso, por meio de um tratamento fenomenológico, investigamos o impacto no desenvolvimento do chuveiro causado por variações na distribuição de pseudorapidez $dN/d\\eta$ de secundários produzidos na colisão primária. Mostramos que diferentemente de quantidades como seção de choque inelástica, multiplicidade, razão de carga e elasticidade, mudanças em $dN/d\\eta$ que preservem tais quantidades são rapidamente diluídas nas sucessivas camadas de interações posteriores à colisão primária. / The behavior of the hadronic interactions at center of mass energies greater than 50 TeV/nucleon is an important source of systematic uncertainty on interpreting data from cosmic ray observatories. In this thesis, we study through Monte Carlo simulations the atmospheric shower observables that could be correlated with different aspects of these interactions. Special attention was paid to the muonic component that is known to be generated from the decay of hadronic particles. The precision and accuracy of a sparse grid of muon counters were studied as a function of the array granularity and the collection area of its cells. In particular, we studied the differences in the radial dependence of the muon density in the shower plane for different models. These differences are shown to be larger in the vicinity of the shower axis and, therefore, could be explored with a detector of sufficiently large dynamic range as to avoid saturation of its acquisition electronics. In addition, through a phenomenological treatment, we investigated the impact on the shower development caused by variations in the distribution of pseudorapidity $ dN/d\\eta $ of secondaries particles produced in the primary collision. We show that unlike quantities such as inelastic cross section, multiplicity, charge ratio and elasticity, changes in $ dN/d\\eta $ that preserve such quantities are rapidly diluted in successive interaction layers subsequent to the primary collision.

Cosmic rays are at the foundation of astroparticle physics and the extensive air showers (EAS) is one indirect way to detect them. Air showers, however, have been used to infer information not just of cosmic rays particles, but also to localize gamma rays sources. The shower maximum of an EAS, defined as the position at the atmosphere where the maximum quantity of charged particles is reached, is an observable of air showers that can permit to infer the mass composition of cosmic rays. For this reason, it is important to propose methods to measure it. Several methods to determine the shower maximum have been implemented in the last decades with the development of different kinds of telescopes. This work discusses the possibility of determining the maximum of air showers using imaging atmospheric Cherenkov telescopes (IACT). The Cherenkov telescopes can detect the Cherenkov radiation produced by the interaction of charged particles with the atmosphere. Those Cherenkov photons are projected back into the plane containing the longitudinal development of the air shower. Each plane is saved as a 2D histogram with the longitudinal and lateral development in the vertical and horizontal axis, respectively. A detailed analysis of each 2D histogram is presented and used to obtain the depth of the maximum of the Cherenkov profile. The main effect seen is a decrease in the shower maximum of Cherenkov photons as a function of the telescope position from the shower axis to 150 m. After 150m from the shower axis, there is a constant behavior that is correlated to the real depth of the maximum of an EAS. Based on this constant behavior after 150 m, the shower maximum is reconstructed and it is shown the resolution of the method as a function of the energy, which is around 55 g/cm2 considering just one telescope, and 15 g/cm2 for the best case considering zenith angle of 20 degrees. Moreover, the method is tested with some simulations took from Very Energetic Radiation Imaging Telescope Array System (VERITAS) experiment to compare with the results of our simulations. The resolution of the reconstruction of the shower maximum for proton and iron showers was also done which ranges around 80 g/cm2 for proton and around 30 g/cm2 for iron in the case of 20° of zenith angle. / Os raios cósmicos estão na base da física das astropartículas e os chuveiros atmosféricos extensos (EAS pela sigla em inglês) são uma maneira indireta de detectá-los. Os chuveiros atmosféricos, no entanto, têm sido usados para inferir informações não apenas sobre partículas de raios cósmicos, mas também para localizar fontes de raios gama. A profundidade de máximo num EAS, definido como a profundidade atmosférica onde a quantidade máxima de partículas carregadas é atingida, é um observável de EAS que permite inferir a composição de massa dos raios cósmicos. Por esse motivo, é importante propor métodos para medí-lo. Vários métodos para determinar a profundidade de máximo foram implementados nas últimas décadas com o desenvolvimento de diferentes tipos de telescópios. Este trabalho discute a possibilidade de determinar a profundidade de máximo de chuveiros atmosféricos utilizando os telescópios atmosféricos Cherenkov (IACT). Os telescópios Cherenkov podem detectar a radiação Cherenkov produzida pela interação de partículas carregadas com a atmosfera. Esses fótons Cherenkov são projetados de volta ao plano que contém o desenvolvimento longitudinal do chuveiro. Cada plano é salvo num histograma 2D com o desenvolvimento longitudinal e lateral no eixo vertical e horizontal, respectivamente. Uma análise detalhada de cada histograma 2D é apresentada e usada para obter a profundidade máxima do perfil de emissão de luz Cherenkov. O principal efeito visto é uma diminuição na profundidade de máximo dos fótons Cherenkov do chuveiro como função da posição do telescópio a partir do eixo do chuveiro até 150 m. A partir de 150 m do eixo do chuveiro, há um comportamento constante que está correlacionado com a profundidade real de máximo do EAS. Com base nesse comportamento constante após 150 m, o máximo do chuveiro é reconstruído e é mostrada a resolução do método em função da energia, que é cerca de 55 g/cm2 considerando apenas um telescópio, e 15 g/cm2 para o melhor caso, considerando o ângulo zenital de 20 graus. Além disso, o método é testado com algumas simulações cedidas pelo experimento VERITAS (Very Energetic Radiation Imaging Telescope Array System, pela sigla em inglês) para comparar com os resultados de nossas simulações. Também foi feita a resolução da reconstrução da profundidade de máximo para chuveiros atmosféricos de prótons e ferro, que varia em torno de 80 g/cm2 para prótons e em torno de 30 g/cm2 para ferro no caso chuveiros inclinados a um ângulo de 20°.

ALTO is a project, currently in the research and development phase, with the goal of constructing a Very High Energy (VHE) gamma-ray observatory in the southern hemisphere. It will detect the particle content reaching the ground from the interactions of either VHE gamma rays or cosmic rays in the atmosphere known as extensive air showers. In this thesis, we use an ALTO prototype built at Linneaus University to estimate the vertical muon intensity in Växjö. The atmospheric muons we detect at ground level come from hadronic showers caused by a cosmic ray entering the atmosphere. Such showers are considered background noise in the context of VHE gamma-ray astronomy, and the presence of muons is an important indicator of the nature of the shower, and thus of the primary particle. The measurement is done by isolating events that produce signals in two small scintillation detectors that are part of the ALTO prototype, and are placed almost directly above each other. This gives us a data set that we assume represents muons travelling along a narrow set of trajectories, and by measuring the rate of such events, we estimate the muon intensity. We estimate the corresponding momentum threshold using two different methods; Monte Carlo simulation and calculation of the mean energy loss. The vertical muon intensity found through this method is about 21% higher than commonly accepted values. We discuss some possible explanations for this discrepancy, and conclude that the most likely explanation is that the isolated data set contains a significant number of “false positives”, i.e., events that do not represent a single muon following the desired trajectory.