Study of the dipolar anisotropy of cosmic rays detected at the Pierre Auger Observatory and its dependence on the declination

Orientador: Carola Dobrigkeit ChinellatoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb WataghinResumo: Esta dissertação apresenta uma análise da distribuição das direções de chegada de raios cósmicos detectados pelo Observatório Pierre Auger, localizado na Argentina, entre primeiro de janeiro de 2004 e 31 de agosto de 2016. Todos os eventos considerados possuem energias maiores que 4 EeV e um ângulo zenital máximo de 80°. Trabalhos anteriores em larga escala angular indicaram a presença de uma anisotropia dipolar na direção de chegada de raios cósmicos para energias maiores que 8 EeV. Este trabalho apresenta um estudo de anisotropia dipolar dividindo o céu em cinco faixas de declinação. Cada uma das faixas é analisada com o objetivo de determinar se uma das faixas é a única responsável pela anisotropia. Este trabalho está dividido em quatro capítulos. O primeiro capítulo apresenta uma introdução sobre raios cósmicos e suas características principais, como o espectro diferencial de energia, a composição química, chuveiros atmosféricos e uma breve discussão sobre a radiação Cherenkov. O segundo capítulo é uma introdução ao Observatório Pierre Auger, apresentando informações sobre os dois tipos de detectores -- o detector de superfície e o detector de fluorescência e como são realizadas as reconstruções da direção de chegada de um evento e da energia associada a esse evento. O terceiro capítulo apresenta uma discussão sobre o estudo de anisotropia dipolar em larga escala angular utilizando a análise modificada de Rayleigh em duas coordenadas angulares, permitindo dessa forma a reconstrução tridimensional do vetor do dipolo. O quarto capítulo apresenta análises dividindo o céu em faixas de declinação e apresenta três métodos diferentes para o estudo de uma anisotropia dipolar. O primeiro método apresentado é a análise de Rayleigh em ascensão reta e a reconstrução da projeção equatorial do dipolo. O segundo método consiste em uma reconstrução tridimensional a partir da intensidade dos raios cósmicos e o terceiro método permite reconstruir a anisotropia dipolar expandindo a distribuição das direções de chegada de raios cósmicos em esféricos harmônicos e estimando os coeficientes dessa expansãoAbstract: This dissertation presents an analysis of the arrival directions of cosmic rays detected by the Pierre Auger Observatory, located in Argentina, between 1 January 2004 and 31 August 2016. All events considered in the analyses have energy greater than 4 EeV and a maximum zenith angle of 80°. Previous works in large angular scale indicated the presence of a dipolar anisotropy in the arrival directions of cosmic rays for energies greater than 8 EeV. This work presents a study of dipolar anisotropy slicing the sky into declination bands. Each one of the bands is analyzed with the goal to determine if a single one of the bands is the responsible for the anisotropy. This work is divided into four chapters. The first chapter presents an introduction about cosmic rays and its main characteristics, like the differential energy spectrum, the chemical composition, air-showers properties and a brief discussion about the Cherenkov radiation. The second chapter is an introduction to the Pierre Auger Observatory and presents information about the two types of detectors -- the surface detector and the fluorescence detector and how the arrival direction and energy reconstructions of an event are made. The third chapter presents a discussion about the study of dipolar anisotropy in large angular scale using the modified Rayleigh analysis in two angular coordinates, thus allowing the tridimensional reconstruction of the dipolar anisotropy. The fourth chapter presents an analysis slicing the sky into declination bands and presents three different methods for the study of dipolar anisotropy. The first method is the Rayleigh analysis in right ascension and the reconstruction of the equatorial projection of the dipole. The second method includes a tridimensional reconstruction from the cosmic-ray intensity and the third method consists of the reconstruction of the dipolar anisotropy expanding the distribution of arrival directions of cosmic rays in spherical harmonics and estimating the expansion coefficientsMestradoFísicaMestra em Física131959/2016-6CNP

The dynamic range of the upgraded surface-detector stations of AugerPrime

The detection of ultra-high-energy cosmic rays by means of giant detector arrays is often limited by the saturation of the recorded signals near the impact point of the shower core at the ground, where the particle density dramatically increases. The saturation affects in particular the highest energy events, worsening the systematic uncertainties in the reconstruction of the shower characteristics. The upgrade of the Pierre Auger Observatory, called AugerPrime, includes the installation of an 1-inch Small PhotoMultiplier Tube (SPMT) inside each water-Cherenkov station (WCD) of the surface detector array. The SPMT allows an unambiguous measurement of signals down to about 250m from the shower core, thus reducing the number of events featuring a saturated station to a negligible level. In addition, a 3.8m2 plastic scintillator (Scintillator Surface Detector, SSD) is installed on top of each WCD. The SSD is designed to match the WCD (with SPMT) dynamic range, providing a complementary measurement of the shower components up to the highest energies. In this work, the design and performances of the upgraded AugerPrime surface-detector stations in the extended dynamic range are described, highlighting the accuracy of the measurements. A first analysis employing the unsaturated signals in the event reconstruction is also presented

Investigating multiple elves and halos above strong lightning with the fluorescence detectors of the Pierre Auger Observatory

ELVES are being studied since 2013 with the twenty-four FD Telescopes of the Pierre Auger Observatory, in the province of Mendoza (Argentina), the world’s largest facility for the study of ultra-high energy cosmic rays. This study exploits a dedicated trigger and extended readout. Since December 2020, this trigger has been extended to the three High levation Auger Telescopes (HEAT), which observe the night sky at elevation angles between 30 and 60 degrees, allowing a study of ELVES from closer lightning. The high time resolution of the Auger telescopes allows us to upgrade reconstruction algorithms and to do detailed studies on multiple ELVES. The origin of multiple elves can be studied by analyzing the time difference and the amplitude ratio between flashes and comparing them with the properties of radio signals detected by the ENTLN lightning network since 2018. A fraction of multi-ELVES can also be interpreted as halos following ELVES. Halos are disc-shaped light transients emitted at 70-80 km altitudes, appearing at the center of the ELVES rings, due to the rearrangement of electric charges at the base of the ionosphere after a strong lightning event

Studies of the mass composition of cosmic rays and proton-proton interaction cross-sections at ultra-high energies with the Pierre Auger Observatory

In this work, we present an estimate of the cosmic-ray mass composition from the distributions of the depth of the shower maximum (Xmax) measured by the fluorescence detector of the Pierre Auger Observatory. We discuss the sensitivity of the mass composition measurements to the uncertainties in the properties of the hadronic interactions, particularly in the predictions of the particle interaction cross-sections. For this purpose, we adjust the fractions of cosmic-ray mass groups to fit the data with Xmax distributions from air shower simulations. We modify the proton-proton cross-sections at ultra-high energies, and the corresponding air shower simulations with rescaled nucleus-air cross-sections are obtained via Glauber theory. We compare the energy-dependent composition of ultra-high-energy cosmic rays obtained for the different extrapolations of the proton-proton cross-sections from low-energy accelerator data

Study of downward Terrestrial Gamma-ray Flashes with the surface detector of the Pierre Auger Observatory

The surface detector (SD) of the Pierre Auger Observatory, consisting of 1660 water-Cherenkov detectors (WCDs), covers 3000 km2 in the Argentinian pampa. Thanks to the high efficiency of WCDs in detecting gamma rays, it represents a unique instrument for studying downward Terrestrial Gamma-ray Flashes (TGFs) over a large area. Peculiar events, likely related to downward TGFs, were detected at the Auger Observatory. Their experimental signature and time evolution are very different from those of a shower produced by an ultrahigh-energy cosmic ray. They happen in coincidence with low thunderclouds and lightning, and their large deposited energy at the ground is compatible with that of a standard downward TGF with the source a few kilometers above the ground. A new trigger algorithm to increase the TGF-like event statistics was installed in the whole array. The study of the performance of the new trigger system during the lightning season is ongoing and will provide a handle to develop improved algorithms to implement in the Auger upgraded electronic boards. The available data sample, even if small, can give important clues about the TGF production models, in particular, the shape of WCD signals. Moreover, the SD allows us to observe more than one point in the TGF beam, providing information on the emission angle

International Masterclasses as part of the Pierre Auger Observatory program of Outreach and Education

The Pierre Auger Observatory is committed to bringing education and knowledge of cosmic rays to the public, with a strong focus on schools and students. Over the last few years, initiatives have been developed, such as the Science Fair, virtual visits, and participation in international activities on the subject of cosmic rays, including collaborations with external groups. Modern digital tools bringing novel ways of interacting with the public have been explored at these initiatives and also locally at a renewed Visitor Center in Malargüe. The development of tools for the public release of the Auger data, including standardized data formats, analysis notebooks, and a 3D interactive event display, led to the creation of a new activity directed to high-school students called Masterclasses. The participants are challenged to perform the reconstruction and selection of events using a graphical interface with 3D effects, then combined into a smoothed, exposure-corrected sky map of arrival directions. A final discussion takes place in which the students engage with peers and scientists, looking for answers about the origin of ultra-high-energy cosmic rays. The concept had a successful debut in 2022 and was included in the 2023 edition of the International Masterclasses on Particle Physics, reaching students worldwide