Speaker
Description
The Pierre Auger Observatory has been measuring extensive air showers produced by ultra-high-energy cosmic rays (UHECRs) for over two decades. While significant progress in this field has been made, the sources, acceleration mechanisms, and hadronic interactions at these energies still remain poorly understood. A key property for constraining these open questions is the mass composition of the primary particles. By detecting the longitudinal profiles of the air showers, the mass composition can be inferred from the distributions of the depth of the shower maximum, Xmax, the atmospheric depth at which the shower reaches its maximum energy deposition. Using 18 years of high-quality profiles measured with the Fluorescence Detector, the Pierre Auger Collaboration has performed a detailed study of the mass composition above 10^17.7 eV. In this talk, we summarize the main results of this analysis and discuss their implications for the origin and nature of UHECRs.
