AugerPrime: The Pierre Auger Observatory Upgrade.
The Pierre Auger Observatory with its exposure provides us with a large set of excellent data. The analysis of these data has led to major breakthroughs in the last decade, but a coherent interpretation has not yet been achieved. New questions have emerged, including that of the composition of cosmic rays in the energy region of the flux suppression, which is of key importance for making progress. To answer these questions, the Observatory has started a major upgrade, called AugerPrime. The main goal of AugerPrime is to improve the mass composition sensitivity using the surface detectors. At the end of 2016 an Engineering Array of the upgraded detectors has been installed and has taken data since then. In this work, the detectors upgrade will be presented. The expected performance and the improved physics sensitivity of the Observatory will be discussed together with the first data collected with the Engineering Array.