AugerPrime: the Pierre Auger Observatory Upgrade

The world largest exposure to ultra-high energy cosmic rays accumulated by the Pierre Auger Observatory led to major advances in our understanding of their properties, but the many unknowns about the nature and distribution of the sources, the primary composition and the underlying hadronic interactions prevent the emergence of a uniquely consistent picture. The new perspectives opened by the current results call for an upgrade of the Observatory, whose main aim is the collection of new information about the primary mass of the highest energy cosmic rays on a shower-by-shower basis. The evaluation of the fraction of light primaries in the region of suppression of the flux will open the window to charged particle astronomy, allowing for composition-selected anisotropy searches. In addition, the properties of multiparticle production will be studied at energies not covered by man-made accelerators and new or unexpected changes of hadronic interactions will be searched for. After a discussion of the motivations for upgrading the Pierre Auger Observatory, a description of the detector upgrade is provided. We then discuss the expected performances and the improved physics sensitivity of the upgraded detectors and present the first data collected with the already running Engineering Array.Comment: 9 pages, 11 figures, presented at UHECR 2018 (Paris, Oct 2018

Astroparticle and particle physics at ultra-high energy: results from the Pierre Auger Observatory

The scientific achievements of the Pierre Auger Collaboration cover diverse and complementary fields of research. The search for the origin of ultra-high energy cosmic rays (UHECRs) is based on the measurement of the energy spectrum and mass composition of the primaries, on studies of multi-messengers, and on extensive anisotropy searches. With the collected data it is also possible to explore the characteristics of hadronic interactions at energies unreachable at human-made accelerators, and to assess the existence of non-standard physics effects. A selection of the latest results is presented and the emerging picture is discussed.Comment: Submission to SciPost Phys. Pro

Auger Highlights

The Pierre Auger Observatory has been designed to investigate the origin and nature of the ultra high energy cosmic rays using a hybrid detection technique. A review of selected results is presented, with the emphasis given to the measurement of energy spectrum, mass composition and arrival directions

Experimental results on cosmic ray composition and energy spectrum around the knee from EAS experiments

The most recent experimental results on cosmic ray composition and energy spectrum from Extensive Air Shower arrays are reviewed and discussed. All experiments agree on the presence of the knee in the energy spectrum at an energy Ek 3 · 1015 eV; the bend is seen in all the shower components, whose study gives consistent results and do not suggest any change in hadronic interactions at these energies. An astrophysical origin for the knee is thus favoured. Most experiments agree on a primary mass composition getting heavier above the knee, but contradicting data also exist. In particular the results based on the observation of the atmospheric ˇCerenkov light, the component more strictly related to the total primary energy, seem to suggest an opposite trend