The Snowmass UHECR white paper: A community roadmap for the next 2 decades

As part of the US “Snowmass” process, the Ultra-High-Energy Cosmic Ray (UHECR) community came together to lay out the current status and open questions of the field and to define a roadmap for the next 2 decades in the context of particle physics and astrophysics. The white paper entitled “Ultra-High Energy Cosmic-Rays: at the Intersection of the Cosmic and Energy Frontiers” was written and published as a special issue of Astroparticle Physics (Astropart.Phys. 147 (2023) 102794 – arXiv:2205.05845). The document evaluated what upgraded and new instrumentation was needed to address the major scientific questions in UHECR physics and provided an integrated timeline for these instruments.

The initial progress to answer these questions will be made by the upgraded Pierre Auger Observatory and Telescope Array experiment in this decade, followed by next generation detectors which can be grouped into one of two categories: 1) high-accuracy ones, such as the Global Cosmic Ray Observatory for the highest energies and IceCube-Gen2 with its surface array for PeV-EeV cosmic rays, aimed to increase statistics for particle physics and rigidity-based galactic and extra-galactic astrophysics, and 2) others that maximize the exposure at the highest energies, such as Probe Of Multi-Messenger Astrophysics, a proposed dual satellite mission, and the Giant Radio Array for Neutrino Detection, a ground based instrument.

In this talk we provide an overview with a focus on the proposed upgrades and new instruments to answer the identified open questions while the astrophysics and particle physics aspect will be discussed in detail in two individual contribution within this session.