Medida de la anisotropía de los rayos cósmicos con ams-02 en la estación espacial internacional

  1. Molero González, Miguel
Dirigida por:
  1. Jorge Casaus Armentano Director/a
  2. Miguel Ángel Velasco Frutos Director/a

Universidad de defensa: Universidad Autónoma de Madrid

Fecha de defensa: 14 de julio de 2021

Tribunal:
  1. Francisco Javier Berdugo Pérez Presidente/a
  2. Daniele Gaggero Secretario/a
  3. Juan Abel Barrio Uña Vocal

Tipo: Tesis

Resumen

The measurement of the charged cosmic ray spectra has provided over the years an important piece of information to understand the acceleration and propagation mechanisms of high energy particles in the cosmos. Among the different types of experiments, space-borne detectors profit from their identification and energy reconstruction capabilities to search for deviations or additional contributions in the fluxes that may challenge the standard paradigm of cosmic rays. In particular, the study of antimatter in space is a very interesting channel since its production is assumed to have a pure secondary origin and, therefore, any excess may constitute a sign of new physical processes. As of today, AMS-02 has provided the most precise measurements of the individual positron and electron fluxes and of the primary galactic cosmic rays in the GeV-TeV energy range. The positron flux shows a significant excess starting from 25 GeV that cannot be fully explained with the traditional models. The electron flux exhibits a significant excess starting from 42 GeV compared to the lower energy trends, but the nature of this excess is different from the positron one. Protons and light primary nuclei show a progressive hardening above ~ 200 GV. The aforementioned observations challenge the current understanding of the acceleration and propagation mechanisms. The origin of these features remains unclear, and a plethora of models have been proposed. In the case of positrons, the additional contribution cannot be explained by a pure secondary component and the inclusion of nearby primary sources is necessary, whether of astrophysical (pulsars) or a more exotic (dark matter) origin. The annihilation or decay of dark matter into Standard Model particles may produce an excess of antimatter particles in cosmic rays, thus allowing for an indirect search of dark matter. In the case of protons and light nuclei, the spectral features could also be explained with the inclusion of local sources of high energy cosmic rays or the modification of the current propagation models. In all the cases, the study of the arrival directions of the individual particle species may help to understand the origin of the observed features and, in particular, allows to explore the impact that nearby sources may imprint in the fluxes. The determination of the large scale anisotropy, at first order described by a dipole, relies on the construction of an isotropic reference map which is compared with the skymap of measured events. The observation of any deviation of this map from the reference might be regarded as a signal. Therefore, the precise understanding of the detector dependences when constructing the reference map is crucial in order to account for possible spurious effects. In this thesis, the techniques developed to construct the isotropic reference map and its application to different cosmic ray species are presented. In particular, results on the dipole anisotropy for electrons, positrons, protons, helium, carbon, and oxygen collected by AMS-02 during its first 8.5 years of operation are reported. The outline of this thesis corresponds to: • Chapter 1 introduces a general review of the cosmic rays as well as observations and challenges to the standard paradigm. This chapter also presents an overview of the anisotropy measurements and motivates the search for anisotropies with AMS-02. • Chapter 2 presents the AMS-02 experiment with a description of each subdetector as well as the data acquisition system and Monte Carlo simulation. • Chapter 3 provides the framework used for the computation of the fluxes as a function of the energy and direction of the incoming particles. The determination of the directionality of the fluxes requires the definition of a set of coordinate systems and statistical tools to obtain and interpret the possible signal. • Chapter 4 describes the application of the framework introduced in chapter 3 to positrons and electrons. The chapter is divided in two parts: the first part describes the standard method used to obtain the intermediate results published in Physical Review Letters; the second one presents the optimization of the analysis based on a template fit to separate positrons and electrons from the proton background. • Chapter 5 presents the anisotropy measurement for protons and light primary nuclei helium, carbon, and oxygen. A detailed description of the method for the light primary nuclei is discussed. • Appendices provide additional details of the work presented in this thesis as well as the tables of the numerical results for each cosmic ray species.