Ultra-High Energy Cosmic Rays: Recent Results and Future Plans of Auger

TL;DR

Recent results from the Pierre Auger Observatory challenge classical views on ultra-high energy cosmic rays, suggesting they mainly reflect the maximum energies of extragalactic accelerators, prompting upgrades for better composition and particle physics measurements.

Contribution

The paper reviews recent observational findings that question traditional interpretations of cosmic ray flux suppression and discusses the AugerPrime upgrade to enhance measurement capabilities.

Findings

Flux suppression above 5x10^{19} eV may not be solely due to the GZK effect.

Data indicates cosmic rays mainly reflect maximum energies of extragalactic sources.

Upgrades will enable composition measurements in the flux-suppression region.

Abstract

Over the last decade a number of important observational results have been reported using data from the Pierre Auger Observatory. We shall review some of the recent key findings that have significantly advanced our understanding of ultra-high energy cosmic rays and that have called into question the `classical' interpretation of the flux-suppression above 5x10^{19} eV as being caused (solely) by the Greisen-Zatsepin-Kuzmin effect. Instead, the data suggest seeing mostly the maximum energy of extragalactic cosmic ray accelerators. This has a number of implications, ranging from reduced prospects of doing particle physics with cosmogenic neutrinos to reduced chances of seeing the sources of ultra-high energy cosmic rays at all. To address these emerging and pressing scientific questions, the Pierre Auger Observatory is presently being upgraded to AugerPrime. It will enable composition measurements into the flux-suppression region and also improve the particle physics capabilities. An Engineering Array has been deployed and is taking data. Full construction will start late 2017.