The Ultra-High-Energy Cosmic Ray (UHECR) community outlined the current status, open questions, and roadmap for the field of UHECRs in the white paper titled "Ultra-High Energy Cosmic-Rays: The Intersection of the Cosmic and Energy Frontiers" (Astropart. Phys. 147 (2023) 102794 - arXiv:2205.05845).
In this paper, the community identified two types of next-generation detectors: (1) high-accuracy detectors and (2) detectors that maximize exposure at the highest energies such as the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA), a proposed dual satellite mission for observing UHECRs and Very High Energy Neutrinos (VHENs).
A key milestone towards such a mission is POEMMA-Balloon with Radio (PBR), designed as a payload for a NASA suborbital Super Pressure Balloon that will circle over the Southern Ocean for up to 100 days. PBR aims to achieve three major science goals: (1) to observe UHECRs via the fluorescence technique from suborbital space; (2) to study high-altitude horizontal air showers (HAHAs) with energies above the cosmic ray knee (E > 3 PeV) using optical and radio detection for the first time; and (3) to follow astrophysical event alerts in the search for VHENs. With a telescope design almost identical to POEMMA, PBR will validate the POEMMA design and proposed analysis strategies.
This contribution presents a brief overview of the PBR detector design, its expected performance, and the current status of the mission.