Publicación: Análisis de los datos iniciales del detector AUGERPRIME
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TESIS DOCTORAL
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Fil: Taboada Nuñez, Alvaro. Comisión Nacional de Energía Atómica; Argentina
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eng
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Los rayos cósmicos siguen entrañando misterios tras casi un siglo desde su descubrimiento. Cuestiones como su origen y propagación por el cosmos, han despertado el interés de generaciones de científicos y que a día de hoy todavía buscan respuesta. Numerosos marcos teóricos han sido desarollados con el afán de entender cómo estas partículas alcanzan energías tan altas, las más elevedas conocidas en el Universo. Para explicar los diferentes aspectos de su espectro de energía, se precisa del entendimiento de los campos mágneticos que interfieren en su propagación y cuyo conocimiento es limitado. La interpretación de las observaciones de las lluvias de partículas generadas por rayos cósmicos en la atmósfera, a menudo requiere de la utilización de simulaciones, las cuales dependen de modelos de interacciones hadrónicas. La observación de un déficit en el número de muones predicho por los modelos supone un grado de complejidad añadido que motiva la sinergia entre la física estudiada en los aceleradores de partículas y la astrofísica. El conocimiento de la composición química de los rayos cósmicos que llegan a la atmósfera es una pieza clave para dar respuesta a estos entresijos. El Observatorio Pierre Auger es actualmente el experimento más grande del mundo dedicado a la observación de rayos cósmicos. Cubre un area de más de 3000 km2 , desplegada con
detectores de partículas que emplean un método de detección híbrido. Por un lado, el Detector de Fluorescencia dispone de telescopios que miden el desarrollo longitudinal de las lluvias de partículas en la atmósfera. Por otro lado, el Detector de Superficie mide la densidad de partículas que llegan al suelo por medio de la utilización de detectores Cherenkov en agua (WCD). De este modo se pueden estimar la energía y la composición química de la partícula originaria de la lluvia. Sin embargo, el número de mediciones con información acerca de la composición a las más altas energías se ve limitado debido al reducido tiempo de operación del Detector de Fluorescencia. Es por ello que se está realizando una mejora del Detector de Superficie con el fin de incrementar su sensibilidad a la composición. Este proyecto recibe el nombre de AugerPrime y tiene como eje principal la instalación de un detector de centelleo (SSD) en cada uno de los detectores Cherenkov en agua. Los dos detectores proporcionan una medida complementaria,
la cual facilita la separación entre las componentes muónica y electromagnética de la lluvia. A finales del año 2016, doce de estos detectores comenzaron la adquisición de datos. A mayores, durante marzo de 2019 setenta y siete más fueron desplegados, incrementando así el número de lluvias observadas a altas energías. Este trabajo tiene por objetivo principal el análisis de los datos de estos detectores. El trabajo presentado en esta tesis doctoral incluye métodos desarrollados para la reconstrucción de lluvias medidas con los detectores de centelleo así como el análisis de los primeros datos obtenidos. Se abordan los siguientes puntos: 1. Estudio de la calibración del SSD en base a simulaciones. 2. Implementación del SSD en la cadena de reconstrucción del Detector de Superficie. 3. Desarrollo de algoritmos para el estudio de la composición química utilizando el WCD y el SSD. 4. Ánalisis de los primeros datos obtenidos por los detectores durante la fase de prueba. 5. Primera estimación de la composición química utilizando datos de los detectores de AugerPrime. Las herramientas desarrolladas en el marco de este trabajo suponen un precedente para para los futuros análisis llevados a cabo en el contexto de AugerPrime.
Despite their discovery almost one hundred years ago, the physics of cosmic rays is still a mystery. Huge efforts have been employed over the last decades in order to understand their origin and propagation through the cosmos until they reach the Earth. Several astrophysical scenarios were developed aiming to explain how cosmic rays can be accelerated up to such high energies, which are orders of magnitude above the ones achieved by man-made accelerators. The different features observed in the measured energy spectrum such as the flux suppression at the highest energies or the region thought to be a transition between galactic and extra-galactic origin remain unclear. The need of models for the magnetic fields at the source environment and acting on the cosmic rays during propagation adds a further complication. The interpretation of measurements from extensive air showers induced by cosmic rays often requires the usage of simulations based on LHC-tuned models for the hadronic interactions. The observation of a deficit in the number of muons predicted by these models is also an unclear issue. Knowing the mass composition of cosmic rays at the top of the atmosphere is of key importance in order to answer these questions. The Pierre Auger Observatory is currently the largest experiment dedicated to the measurement of ultra-high-energy cosmic rays. Covering more than 3000 km2 with ground-based detectors, it employs a hybrid detection technique of air showers. The Fluorescence Detector uses telescopes for measuring the longitudinal profile of showers as they develop in the atmosphere. The Surface Detector measures the footprint of showers at the ground by sampling lateral distributions of particles with water-Cherenkov detectors (WCDs). This allows us to estimate the energy and the mass composition of the primary particle. However, the reduced duty cycle of the Fluorescence Detector limits the statistics of mass-sensitive measurements at the highest en- ergies. In order to achieve the aforementioned goals, the observatory is currently undergoing a detector upgrade, named AugerPrime, which aims to enhance the mass-sensitivity of the Surface Detector by placing a plastic scintillator on top of each of the water-Cherenkov detectors. This Scintillator Surface Detector (SSD) provides with a complementary measurement thus allowing for the separation of the electromagnetic and muonic shower components. By the end of 2016, twelve Surface Detector stations were upgraded as part of an engineering phase. In addition, seventy-seven SSDs were deployed during March 2019 increasing the wealth of showers measured at high energies. The analysis of the data provided by these detectors is the final goal of this work. The work presented in this dissertation includes methods developed for the reconstruction of air showers with the SSDs and the analysis of the first data recorded. 1. Studies of the calibration of the SSD by means of simulating the flux of secondary particles from low energy showers. 2. Inclusion of the SSD into the standard reconstruction methods with the Surface Detector. This implies the study of the lateral distribution of the SSD signals. 3. Development of algorithms for reconstructing the mass composition using information from both the WCD and the SSD reconstructions. 4. Analysis of first data delivered by upgraded detectors during the engineering phase. 5. First estimate of the mass composition using data from AugerPrime detectors. The tools developed in this work will serve as a precedent for future analyses carried out in the context of mass composition with AugerPrime.
Despite their discovery almost one hundred years ago, the physics of cosmic rays is still a mystery. Huge efforts have been employed over the last decades in order to understand their origin and propagation through the cosmos until they reach the Earth. Several astrophysical scenarios were developed aiming to explain how cosmic rays can be accelerated up to such high energies, which are orders of magnitude above the ones achieved by man-made accelerators. The different features observed in the measured energy spectrum such as the flux suppression at the highest energies or the region thought to be a transition between galactic and extra-galactic origin remain unclear. The need of models for the magnetic fields at the source environment and acting on the cosmic rays during propagation adds a further complication. The interpretation of measurements from extensive air showers induced by cosmic rays often requires the usage of simulations based on LHC-tuned models for the hadronic interactions. The observation of a deficit in the number of muons predicted by these models is also an unclear issue. Knowing the mass composition of cosmic rays at the top of the atmosphere is of key importance in order to answer these questions. The Pierre Auger Observatory is currently the largest experiment dedicated to the measurement of ultra-high-energy cosmic rays. Covering more than 3000 km2 with ground-based detectors, it employs a hybrid detection technique of air showers. The Fluorescence Detector uses telescopes for measuring the longitudinal profile of showers as they develop in the atmosphere. The Surface Detector measures the footprint of showers at the ground by sampling lateral distributions of particles with water-Cherenkov detectors (WCDs). This allows us to estimate the energy and the mass composition of the primary particle. However, the reduced duty cycle of the Fluorescence Detector limits the statistics of mass-sensitive measurements at the highest en- ergies. In order to achieve the aforementioned goals, the observatory is currently undergoing a detector upgrade, named AugerPrime, which aims to enhance the mass-sensitivity of the Surface Detector by placing a plastic scintillator on top of each of the water-Cherenkov detectors. This Scintillator Surface Detector (SSD) provides with a complementary measurement thus allowing for the separation of the electromagnetic and muonic shower components. By the end of 2016, twelve Surface Detector stations were upgraded as part of an engineering phase. In addition, seventy-seven SSDs were deployed during March 2019 increasing the wealth of showers measured at high energies. The analysis of the data provided by these detectors is the final goal of this work. The work presented in this dissertation includes methods developed for the reconstruction of air showers with the SSDs and the analysis of the first data recorded. 1. Studies of the calibration of the SSD by means of simulating the flux of secondary particles from low energy showers. 2. Inclusion of the SSD into the standard reconstruction methods with the Surface Detector. This implies the study of the lateral distribution of the SSD signals. 3. Development of algorithms for reconstructing the mass composition using information from both the WCD and the SSD reconstructions. 4. Analysis of first data delivered by upgraded detectors during the engineering phase. 5. First estimate of the mass composition using data from AugerPrime detectors. The tools developed in this work will serve as a precedent for future analyses carried out in the context of mass composition with AugerPrime.