Búsqueda de fotones de ultra-alta energía con el detector de muones AMIGA
2018
| Tesista | Nicolás Martín GONZÁLEZ Licenciado en Ciencias Físicas - Universidad de Buenos Aries - Argentina Dr. en Astrofísica - Instituto Sabato UNSAM/CNEA - Argentina PhD in Astrophysics - Karlsruhe Institute of Technology (KIT) - Alemania |
| Director | Dr. Alberto ETCHEGOYEN. CNEA, UNSAM, CONICET - Argentina |
| Codirector | Dr. Johannes BLÜMER. KIT - Alemania |
| Lugar de realización | Instituto de Tecnologías en Detección y Astropartículas - Centro Atómico Constituyentes - CNEA - Argentina Instituto de Tecnología de la Universidad Nacional de Karlsruhe - Alemania |
| Fecha Defensa | 209/02/2018 |
| Jurado | Dr. Thomas SCHWETZ-MANGOLD. KIT - Alemania Dr. Thomas MÜLLER. KIT - Alemania Dr. Xavier BERTOU. CNEA, CONICET - Argentina Dr. Alberto Daniel SUPANITSKY. IAFE, UTN, CONICET - Argentina |
| Código | IS/TD 111/18 |
Título completo
Búsqueda de fotones de ultra-alta energía con el detector de muones AMIGA
Resumen
Los rayos cósmicos son conocidos desde hace más de 70 años y, sin embargo, su origen sigue siendo un misterio. Del mismo modo, la posibilidad de una componente fotónica de muy alta energía es uno de los problemas abiertos en la Astrofísica. La búsqueda de fotones de alta energía complementa las mediciones de los rayos cósmicos y neutrinos hacia una comprensión multi-canal de los fenómenos astrofísicos más energéticos.
En la búsqueda de fotones de ultra-alta energía, es crucial definir parámetros sensibles a la composición capaces de rechazar adecuadamente el fondo hadrónico de los rayos cósmicos. El contenido muónico de las lluvias atmosféricas extensas producidas por los rayos cósmicos primarios al entrar en la atmósfera es uno de los aspectos más prometedores en este sentido. El detector de muones subterráneo AMIGA, como parte de la próxima mejora AugerPrime del Observatorio Pierre Auger, ofrece una oportunidad única y directa para medir muones de alta energía de lluvias atmosféricas extensas, y así, aumentar la sensibilidad del Observatorio a una señal fotónica primaria.
El objetivo principal de esta tesis es la extensión de la búsqueda de fotones de ultra alta energía hasta ~1016.5 eV. En este marco, definimos y describimos dos nuevos observables sensibles a la composición diseñados para la discriminación fotón/hadrón para ser aplicados en el detector de superficie y detector de muones del Observatorio Auger para energías mayores a 1016.4 eV. El método multiparamétrico, bautizado Mb+Q , es extensamente estudiado y su ejecución se aborda bajo numerosas condiciones. Se demuestra que el rechazo de fondo y la eficiencia de la señal para el método compuesto son adecuados para imponer los mejores límites superiores de todos los experimentos de rayos cósmicos.
Considerando la alta exposición del experimento Auger en dirección al centro galáctico, el método descrito en esta tesis representa una herramienta valiosa con un potencial de descubrimiento sin precedentes en la detección de una señal fotónica minúscula en el flujo de rayos cósmicos. Se preveé que esta investigación sea la base de una futura publicación oficial de la Colaboración Pierre Auger.
Complete Title
Search for ultra-high energy photons with the AMIGA muon detector
Abstract
Cosmic rays (E>1014 eV) have been known for more than 70 years, and yet their origin remains elusive. Similarly, the possibility of a very-high energy photon component of the cosmic radiation is one of the open problems in Astroparticle Physics. The search for high energy photons complements measurements of cosmic rays and neutrinos towards a multi-messenger understanding of the most energetic astrophysical phenomena. In particular, the discovery of photons with energies between 1016.5 eV and 1018 eV in the cosmic rays flux could be of particular interest not only for the field of Astroparticle Physics, but also for Astrophysics and fundamental Physics, since they are tracers of the highest-energy processes in the Universe.
In the search for ultra-high energy photons, it is crucial to define composition-sensitive parameters capable of adequately rejecting the hadronic cosmic-ray background. The muon content of the extensive air showers produced by primary cosmic rays as they enter the atmosphere is one of the most promising aspects that could lead to the best possible discrimination between photons and hadronic cosmic rays. The AMIGA underground muon detector, as a part of the upcoming AugerPrime upgrade for the Pierre Auger Observatory, offers a unique and straight-forward opportunity to directly measure high-energy muons of extensive air showers, and thus, enhance the sensibility of the Observatory to a primary photon signal.
The Pierre Auger Collaboration has proposed several parameters in order to study a possible ultra-high energy photon component in the hadronic cosmic-ray flux. However, the non-observation of photon candidates resulted in upper limits for energies above 1018 eV. On the other hand, the energy window between 1016.5 eV and 1018 eV has only been explored by the KASCADE-Grande and the EAS-MSU experiments which impose upper limits to the photon flux. Currently, this energy domain is not explored by the Pierre Auger Observatory.
The main objective of this thesis is the extension of the ultra-high energy photon search down to ~1016.5 eV. The stringent theoretical and experimental upper limits to the photon flux at these energies make the search of a weak photon signal in the vast hadronic cosmic-ray background a challenging task. Therefore, parameters sensitive to the predominantly electromagnetic signal from photon primaries are of paramount importance. In this framework, we define and describe two new composition-sensitive observables designed for the photon/hadron discrimination quest in order to either detect photon primaries in the 1016 eV energy domain or improve the upper limits established by previous experiments.
The observable Mb combines the muon densities measured by the AMIGA underground muon stations and their distance to the shower axis, similarly to the well-known Sb parameter used previously in photon searches by the Pierre Auger Collaboration. On the other hand, the observable Q exploits the difference in the slope of the lateral distribution of particles between photon- and hadron-initiated showers. In the latter case, the showers are expected to develop higher in the atmosphere and thus they arrive to the ground with a flatter distribution of particles.
In this work, we tune both observables to be applied in the surface and muon detector of the Auger Observatory for energies above Erec = 1016.4 eV and θ<45° . A multiparametric method, baptized Mb +Q , is extensively studied and its performance is addressed under numerous conditions. The background rejection and the signal efficiency for the compound method is proved to be suitable to impose the best upper limits of all the cosmic-ray experiments with only a few years of data, and particularly improve them by one order of magnitude by the end of Auger planned operation at December 31st 2025 . Considering the high exposure of the Auger experiment in the direction of the Galactic center, the method described in this thesis represents a valuable tool with an unprecedented discovery potential in the detection of a minuscule photon signal in the cosmic-ray flux. Although a blind estimation of the sensitivity to a photon flux is presented in this research, the application to data is foreseen to be carried out in the near future for a dedicated full-author list paper of the Pierre Auger Collaboration
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