Speaker
Description
The Pierre Auger Observatory has achieved unprecedented precision in measurements of mass-sensitive air-shower observables of ultra-high-energy cosmic rays (UHECRs). These measurements provide important constraints on their origin and propagation, as well as on the production of secondary particles at the highest energies. In particular, the depth of shower maximum, $X_{\rm max}$, and its fluctuations provide strong sensitivity to the mass composition over a broad energy range. The energy evolution of this observable indicates a transition in the UHECR mass composition with increasing energy, with the quantitative interpretation depending on the modeling of hadronic interactions in extensive air showers. These measurements are also relevant for the interpretation of high-energy neutrino observations and limits. Combined with the energy spectrum, they can be used to inform models of UHECR elemental abundances at sources and their interaction processes in propagation, which in turn determine the production of secondary neutrinos. In particular, the composition of the UHECR flux influences predictions for cosmogenic neutrinos and enters the interpretation of possible connections between UHECR sources and astrophysical neutrinos. In this contribution, we will provide an overview of mass-composition measurements at the Pierre Auger Observatory and discuss their relevance for high-energy neutrino studies.