The Global Cosmic-ray Observatory (GCOS)

The Global Cosmic-ray Observatory (GCOS) is a planned next-generation large-scale observatory designed to study ultra-high-energy cosmic rays, neutrinos, and photons. GCOS will be a multi-site project to deliver comprehensive sky coverage, with locations in the western United States under consideration for one of the sites. The core of its scientific goals is to measure the properties of the highest-energy particles and particle interactions thus far seen in nature with unparalleled precision while also definitively identifying their sources through unprecedented statistics. This combination will allow GCOS to simultaneously push the horizon of particle physics and astrophysics. To achieve this, the observatory will necessitate the development of new higher fidelity detectors and, when all sites are combined, will require an aperture at least ten times larger than existing facilities. Planning for this project is underway, with operations projected to commence in the 2030s, aligning well with the phased decommissioning of current detectors. This presentation outlines the scientific rationale behind GCOS, provides an update on the project's status, discusses early design concepts, and offers preliminary estimates of its scientific capabilities and reach.