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
