AugerPrime: Status and first results

Abstract: With the knowledge and statistical precision derived from two decades of measurement, the Pierre Auger Observatory has significantly deepened our understanding of ultra-high-energy cosmic rays while unearthing an increasingly complex astrophysical landscape and exposing tensions with hadronic interaction models. The field now demands the mass of individual cosmic-ray primaries as an observable with an exposure that only the 3000-square-kilometer surface array of the Observatory can provide. Access to the primary mass hinges on the disentanglement of the electromagnetic and muonic components of extensive air showers. To achieve this, scintillator and radio detectors have been installed atop each existing water-Cherenkov detector of the surface array, whose dynamic range has also been enhanced through the installation of small-area PMTs. Additionally, the timing and signal resolution of all detector stations have been improved through upgraded station electronics, and underground muon counters have been installed in a region of the array with denser spacing. As the commissioning of the final components of AugerPrime reaches its conclusion and the enhanced array comes fully online, we present the realization of its design, its performance, and the first results from this now multi-hybrid observatory.