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Project Pierre Auger

Updated: 2020-10-07

Introduction

The subject of scientific research of the Department are cosmic rays, especially in the energy range above 1017 eV. Particles with such high energies – several orders of magnitude higher than the energies achieved in man-made particle accelerators – reach Earth from space. The origin of these ultra-high-energy particles is so far unknown. We don't know where in the Universe are their sources, or how are they accelerated to the extreme energies observed. Nevertheless, there is no doubt that these particles with extremely high energies really do arrive to us from the Cosmos; their origin and acceleration mechanism are one of the greatest puzzles in present–day astrophysics. For experimental studies of these highest-energy cosmic rays, a giant array of cosmic rays detectors was constructed: the Pierre Auger Observatory.

About the project

The Pierre Auger Observatory is located near the town of Malargue in the province of Mendoza, Argentina. It is a hybrid detector that combines a network of surface detectors with a fluorescence detector. The surface detector stations are water Cherenkov detectors – tanks containing 12 m3 of water. These tanks are placed 1.5 km apart. Each station, powered by solar batteries, counts particles hitting the water tank. Particles from an extensive air shower arrive at several stations almost simultaneously. The observatory consists of 1600 particle detectors, which form a gigantic network covering about 3000 km2.

A second detection system uses the faint glow (fluorescence) caused by the collisions of shower particles with air molecules. On dark, moonless nights, finely tuned light sensors can measure this fluorescence. A collection of light sensors pointing around the sky makes an effective air shower detector, observing an air shower as a trace of light across the sky. The total amount of light depends on the number of particles in the shower, which in turn depends on the energy of the primary cosmic ray particle initiating that shower in the atmosphere. The system consists of 4 fluorescence detectors, each containing 6 telescopes. The fluorescence detectors observe the sky above the area covered by the network of surface detectors.

Purpose of research

The main goal of the Pierre Auger Project is a detailed study of the energy spectrum, of the distribution of cosmic ray arrival directions at the highest observed energies, as well as (at least partial) identification of cosmic ray composition. To achieve this goal, it is necessary to collect as large a sample as possible of cosmic rays events in the extremely high energy range (above 1019 eV). Gathering such data will help to solve the mystery of the origin of ultra-high-energy cosmic rays. The main experimental difficulty is that particles with very high energies are extremely rare: above the energy of 1019 eV only 1 particle arrives per 1 km2 per year.

IFJ contribution

Physicists from the Department NZ 15 of IFJ PAN were involved in the study of the optical image of the air shower, the analysis of light scattering in the atmosphere and the resulting modification of the air shower image, the study of the impact of local changes in the Earth's atmosphere on the development of air showers, and conducted research on the identification of photons and neutrinos among cosmic rays. Research was carried out on the feasibility of microwave and radar detection of extensive air showers, or the radar detection of extensive air showers.

At present, Physicists from the Department NZ15 of IFJ PAN are concentrating on the works related to the upgrade of the Pierre Auger Observatory, called Auger Prime. In a close, multilateral, international cooperation, and with the help of engineers from the Department of Scientific Apparatus and Infrastructure Construction in IFJ PAN, a technique for assembling and testing SSD detectors was developed for the Pierre Auger Observatory. The assembly and tests of 228 such detectors at the IFJ PAN has been completed [Read more].

Main results

The main results obtained by the Pierre Auger Observatory include:

  • Confirmation of the existence of a strong flux suppression at the highest energies. Its origin is not yet fully explained. This is the most precise measurement of the cosmic-ray energy spectrum at ultra-high energies:
    [Phys. Rev. Lett 125, (2020) 121106, Phys. Rev. D 102, 062005 (2020)].
  • First indication that the primary composition of ultra-high energy cosmic-rays is getting heavier at higher energies: [ PoS(ICRC2019)482].
  • Discovery of a large scale anisotropy in the arrival directions of ultra-high energy cosmic-rays, indicating that their origin is extragalactic:
    [ Science 357 (2017) 1266.].
  • Intermediate scale anisotropies suggested by correlation with different astrophysical catalogs:
    [ApJL 853:L29, 2018].
  • Best upper limit of the flux of neutral elementary particles (neutrinos and photons) of high energy (>1017 eV)); key role in the field of multimessenger astrophysics
    [JCAP 1910 (2019) 022, JCAP 1704 (2017) 009].

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