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Opis: Cosmic rays with energies above 10^18 eV, usually referred to as ultra-high energy cosmic rays (UHECR), have been a mystery from the moment they have been discovered. Although we have now more information on their extragalactic origin, their direct sources still remain hidden due to deviations caused by galactic magnetic fields. Another mystery, apart from their production sites, is their nature. Their mass composition, still uncertain at these energies, would give us a better understanding on their production, acceleration, propagation and capacity to produce extensive air showers in the Earth's atmosphere. Mass composition studies of UHECR try to determine their nature from the difference in development of their extensive air showers. In this work, observational parameters from the hybrid detection system of the Pierre Auger Observatory are used in a multivariate analysis to obtain the mass composition of UHECR. The multivariate analysis (MVA) approach combines a number of mass composition sensitive variables and tries to improve the separation between different UHECR particle masses. Simulated distributions of different primary particles are fitted to measured observable distributions in order to determine individual elemental fractions of the composition. When including observables from the surface detector, we find a discrepancy in the estimated mass composition between a mixed simulation sample and the Pierre Auger data. Our analysis results from the Pierre Auger data are to a great degree independent on hadronic interaction models. Although they differ at higher primary masses, the different models are more consistent, when combining fractions of oxygen and iron. Compared to previously published results, the systematic uncertainty from hadronic interaction models is roughly four times smaller. Our analysis reports a predominantly heavy composition of UHECR, with more than a 50% fraction of oxygen and iron at low energies. The composition is then becoming heavier with increasing energy, with a fraction of oxygen and iron above 80% at the highest energies.
Ključne besede: astroparticle physics, ultra-high energy cosmic rays, extensive air showers, mass composition, Pierre Auger Observatory, machine learning, multivariate analysis
Objavljeno v RUNG: 03.04.2019; Ogledov: 6896; Prenosov: 197
Celotno besedilo (17,53 MB)

Opis: The Pierre Auger Observatory (PAO), the world’s largest cosmic ray detector combines a large surface detector (SD) with an air fluorescence detector (FD). It is designed to observe extensive air showers (EAS) of billions of secondary particles induced by the UHECRs in the earths’ atmosphere. The “hybrid” design (i.e., detected simultaneously by SD and FD) provides wealth of information about shower development and excellent event reconstruction. Together with observations of UHECRs, the Surface Detector (SD) of the PAO is sensitive to UHE neutrinos through the observation of deeply initiated inclined down-going showers produced by neutrino interactions in the atmosphere, which method has been well established. On the other hand, high-energy photons can also be discriminated from background of charged cosmic rays based on their characters of the shower front. In this talk, I will give a review on recent results from PAO and introduce the ultra-high energy multi-messenger studies from PAO.
Ključne besede: Pierre Auger Observatory, cosmic rays, ultra-high energy
Objavljeno v RUNG: 17.01.2018; Ogledov: 4799; Prenosov: 0
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Ključne besede: Pierre Auger Observatory, ultra-high energy cosmic rays (UHECR), UHECR anisotropies, angular power spectrum, needlet wavelet analysis
Objavljeno v RUNG: 23.06.2017; Ogledov: 5541; Prenosov: 0
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Ključne besede: Pierre Auger Observatory, ultra high energy cosmic rays (UHECR), UHECR hybrid detection technique, UHECR energy spectrum, UHECR mass composition, UHECR arrival directions
Objavljeno v RUNG: 20.06.2017; Ogledov: 7611; Prenosov: 398
Celotno besedilo (861,47 KB)

Ključne besede: ultra high energy (UHE) cosmic rays, cosmic ray experiments, Pierre Auger Observatory, UHE photon search
Objavljeno v RUNG: 13.04.2017; Ogledov: 5287; Prenosov: 0
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