XII International Workshop on Ring Imaging Cherenkov Detectors - RICH2025

The Pierre Auger Observatory is the world’s largest cosmic-ray observatory, dedicated to the study of ultra-high-energy (UHE) cosmic rays with energies above 10¹⁷ eV. This overview talk presents recent results and ongoing research across a wide range of topics aimed at elucidating the origin, composition, and interactions of these enigmatic particles. Key highlights include measurements of the energy spectrum—featuring the second knee and the suppression at the highest energies—as well as studies of mass composition derived from the depth of shower maximum and the muon content of inclined air showers. Recent progress in understanding the number of muons and discrepancies with hadronic interaction models has provided new constraints on proton–proton cross sections at centre-of-mass energies beyond those accessible at colliders.

We discuss anisotropy searches in arrival directions, including efforts to identify potential sources through correlations and harmonic analyses, and the ongoing search for UHE photons and neutrinos as signatures of exotic physics and cosmogenic processes. The capability of the Observatory to detect upward-going air showers enables complementary searches for beyond-standard-model particles. Atmospheric monitoring—using lidar scans, the XY-scanner, and aerosol attenuation models—ensures high-precision energy and composition reconstruction, while the inter-calibration of the fluorescence detectors, the surface detectors, and the high-elevation telescopes enhances longitudinal shower profiling.

Additional topics include observations of atmospheric transient phenomena such as elves, halos, and terrestrial gamma-ray flashes, and searches for high-energy neutrons from Galactic sources. Advances in radio detection using the Auger Engineering Radio Array, including interferometric techniques and calibration efforts, have further expanded the multi-hybrid capabilities of the Observatory. Finally, the ongoing AugerPrime upgrade aims to enhance mass composition sensitivity at the highest energies through the addition of radio antennas and surface scintillator detectors, improved electronics, and underground muon detectors. These enhancements will allow the Pierre Auger Observatory to address open questions in cosmic-ray astrophysics and probe new physics at the highest energies accessible in nature.