International agreement for the Pierre Auger Observatory upgrade, and the extension of the studies of nature and origin of the extreme energy cosmic particles for the next 10 years

Nov. 24, 2015

Ultra-high energy cosmic rays are elementary particles and nuclei, which travel across the Universe with energies more than 10 million times higher than the most energetic particles in the man-made accelerators.

Such very rare extreme energy particles are precious messengers about the most violent non-thermal processes in the cosmos, on which our knowledge is still very limited. Amongst the cosmic rays that are constantly bombarding the Earth, there are in average only few ultra-high energy particles arriving at our atmosphere per square kilometer per millennium.

From the year 1994, the researchers of the Laboratory for astroparticle physics of the University of Nova Gorica and of the Experimental particle physics department of the Jožef Stefan Institute in Ljubljana actively participate in the international collaboration Pierre Auger, which has built in Argentina the world’s largest (of the area of 3.000 square kilometers) observatory for studies of the extreme energy cosmic rays. To the detector construction of 56 million dollars cost, more than 40 governmental and other institutions have contributed, amongst which also the Slovenian research agency (ARRS) and the Ministry of Higher Education, Science and Technology of the Republic of Slovenia. The Pierre Auger Observatory, with its grid of 1.660 surface detectors and 24 fluorescence light detectors, measures gigantic showers of relativistic secondary particles that are the result of collisions between the highest-energy cosmic rays and atomic nuclei of the atmosphere. The team of nine researchers from Slovenia contributes now to various researches performed within the Pierre Auger Observatory. The studies of the team are focused on the search of gamma-rays and neutrinos in cosmic rays, since these chargeless particles are not deflected by the cosmic magnetic fields and hence allow to learn about the production sites of the extreme energy cosmic-ray particles. Another domain of Slovenian studies is the search for microscopic black holes amongst the products of interactions of the ultra-high energy cosmic rays in the atmosphere. The results obtained jointly with the colleagues from the Pierre Auger Collaboration reveal, in addition to the extreme energy cosmic ray flux suppression, which is the consequence of the propagation effect known as Greisen-Zatsepin-Kuzmin (GZK) cutoff, also the hints on the limiting energy of the most powerful cosmic particle accelerators.

After 15 years of successful functioning of the Pierre Auger Observatory, a new international agreement for continued operation of the Observatory until 2025 has been signed on 16. november 2015, by the science collaborators and funding agency representatives, gathered at the Observatory site in Malargüe, Argentina. The planned Pierre Auger Observatory upgrade (baptized as AugerPrime) will enhance the 1660 existing surface detectors with new scintillation detectors and new electronics, which will considerably improve the identification of secondary cosmic ray muons, and finally the determination of the mass of the primary ultra-high energy cosmic rays. This new detector capabilities will be of the key importance for understanding the cosmic ray acceleration mechanisms and for identification of the astrophysical sources of the most energetic particles in the Universe.

A prototype station of the upgraded AugerPrime detector in the Argentinian Pampa. To the Water Cherenkov Detector containing 12000 liters of water (bottom), a 4 square meter scintillation detector (top) is added to enhance the cosmic ray particle identification capabilities.
On 16. 11. 2015, a new International Agreement for the Pierre Auger Observatory upgrade and the 10-years extension of its functioning has been signed at the Auger Headquarters in Malargüe, Argentina.
Los Morados, one of the four Fluorescence Detector sites of the Pierre Auger Observatory.