From Ground to Space: An Overview of the JEM-EUSO Program for the Study of UHECRs and Astrophysical Neutrinos

Abstract: The JEM-EUSO (Joint Exploratory Missions for Extreme Universe Space Observatory) collaboration is an international initiative studying ultra-high-energy cosmic rays and related phenomena. These particles, with energies exceeding 10$^{20}$~eV, provide insights into extreme astrophysical processes but remain challenging to detect due to their low flux. At the heart of JEM-EUSO's technology is an ultra-fast, highly sensitive UV camera capable of detecting EASs in the atmosphere with exceptional spatial and temporal resolution. A dedicated Cherenkov camera has been developed to evaluate the viability of the Earth-skimming technique from high altitudes. Fluorescence and Cherenkov detectors can be used together to create a hybrid detection surface. This innovative approach enables detailed studies of fluorescence and Cherenkov light from cosmic ray and neutrino interactions. The JEM-EUSO technology will allow for observations from space to significantly increase the exposure to these rare phenomena. The collaboration employs a multi-platform strategy with ground-based experiments like EUSO-TA calibrating detection systems and validating models, and balloon-borne missions such as EUSO-Balloon and EUSO-SPB1/SPB2 demonstrating observations from the stratosphere and testing technologies. Space-based missions, particularly Mini-EUSO on the ISS, have provided valuable data on UV backgrounds, TLEs, and meteoroids, as well as demonstrating the potential for future space-based detection. While we are developing a cross-platform methodology, we are ultimately moving towards space-based measurements. Future efforts include the POEMMA space mission, designed for stereoscopic observations of UHECRs and multi-messenger phenomena, the PBR experiment, which integrates radio detection and is scheduled to fly in 2027, and the M-EUSO satellite mission, proposed to ESA.