Publication: Mass composition studies from the Azimuthal asymetry in the risetime of the surface detector signals of the Pierre Auger Observatory
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2017-03-29
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Universidad Complutense de Madrid
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Abstract
Este trabajo ha sido desarrollado en el marco de la Colaboracíon Pierre Auger, que actualmente opera el Observatorio ḿas grande del mundo para el estudio de rayos ćosmicos con enerǵıas por encima de 1017 eV. El Observatorio est́a compuesto por un Detector de Superficie (SD), que consiste en 1660 estaciones que miden la componente múonica y electromagńetica de las cascadas, y por un Detector de Fluorescencia (FD) que mide su desarrollo longitudinal. Particularmente, esta tesis est́a dedicada a un estudio completo y actualizado de la asimetŕıa observada en la estructura temporal de las se˜nales del SD con respecto a la direccíon de llegada de la cascada atmosf́erica, con el fin de obtener informacíon acerca de la composicíon en masa de los rayos ćosmicos de ultra-alta enerǵıa (> 1018 eV). Para caracterizar la estructura temporal se usa el paŕametro risetime t1/2, definido como el tiempo que la se˜nal integrada tarda en crecer desde el 10% hasta el 50%. Para este estudio se ha usado la muestra de datos reales detectados por el SD entre Enero de 2004 y Octubre de 2014. Adeḿas, se ha contado con ḿas de 6×105 eventos generados mediante simulaciones Monte Carlo usando distintos modelos hadŕonicos, en part́ıcular QGSJETII-04 y EPOS-LHC. Esta libreŕıa se ha usado para validar el ḿetodo y extraer informacíon de la composicíon en masa. Para llevar a cabo el ańalisis primero se seleccionan eventos en intervalos de enerǵıa E y ́angulo zenital θ. Para cada intervalo se ha calculado el valor medio del risetime dividido por la distancia radial de la estacíon correspondiente ht1/2/ri, y su dependencia con el ́angulo polar ζ ha sido modelada para extraer la amplitud de la asimetŕıa. Para una E primaria dada, la amplitud de asimetŕıa alcanza un ḿaximo en el valor (sec θ)max, que depende de la masa del primario...
This work has been carried out in the framework of the Pierre Auger Collaboration that is presently operating the largest Observatory in the world for the study of cosmic rays with energies over 1017 eV. The Observatory is provided with a Surface Detector (SD) consisting of 1660 stations that measure the muonic and electromagnetic components of the showers, and a Fluorescence Detector (FD) that record their longitudinal development. In particular, this thesis is devoted to study the asymmetry in the time structure of the SD signals with respect to the shower direction, aiming to obtain information about the mass composition of ultra-high energy cosmic rays (> 1018 eV). To characterize the time structure, the risetime parameter t1/2 has been used, which is defined as the time that it takes for the integrated signal to rise from 10% to 50%. For this study, the sample of data collected by the SD between January 2004 to October 2014 has been used. In addition more than 6 × 105 MC simulated events have been generated using several models of hadronic interaction, in particular QGSJETII-04 and EPOS-LHC. This MC library has been used to validate the method and extract information on the mass composition. To carry out the analysis, events are firstly split in intervals of energy E and zenith angle θ. For each interval, the average value of the risetime divided by the core distance of the corresponding station ht1/2/ri has been computed, and its dependence with the polar angle ζ has been modelled to extract the amplitude of the asymmetry. For a given primary E, the asymmetry amplitude reaches a maximum at a (sec θ)max value that depends on the primary mass...
This work has been carried out in the framework of the Pierre Auger Collaboration that is presently operating the largest Observatory in the world for the study of cosmic rays with energies over 1017 eV. The Observatory is provided with a Surface Detector (SD) consisting of 1660 stations that measure the muonic and electromagnetic components of the showers, and a Fluorescence Detector (FD) that record their longitudinal development. In particular, this thesis is devoted to study the asymmetry in the time structure of the SD signals with respect to the shower direction, aiming to obtain information about the mass composition of ultra-high energy cosmic rays (> 1018 eV). To characterize the time structure, the risetime parameter t1/2 has been used, which is defined as the time that it takes for the integrated signal to rise from 10% to 50%. For this study, the sample of data collected by the SD between January 2004 to October 2014 has been used. In addition more than 6 × 105 MC simulated events have been generated using several models of hadronic interaction, in particular QGSJETII-04 and EPOS-LHC. This MC library has been used to validate the method and extract information on the mass composition. To carry out the analysis, events are firstly split in intervals of energy E and zenith angle θ. For each interval, the average value of the risetime divided by the core distance of the corresponding station ht1/2/ri has been computed, and its dependence with the polar angle ζ has been modelled to extract the amplitude of the asymmetry. For a given primary E, the asymmetry amplitude reaches a maximum at a (sec θ)max value that depends on the primary mass...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Atómica, Molecular y Nuclear, leída el 03-03-2016