Status and challenges of the Future Circular Hadron Collider FCC-hh

The Future Circular Collider (FCC) study was launched as a worldwide international collaboration hosted by CERN with the ultimate goal of pushing the energy frontier far beyond the LHC. FCC covers two accelerators, namely an energy-frontier hadron collider (FCC-hh) and a highest luminosity, high-energy lepton collider (FCC-ee) serving as electroweak Higgs factory, as a possible first stage. The mass of particles that could be either directly produced at FCC-hh or indirectly detected at FCC-ee is increased by an order of magnitude, relative to today's reach, and the subatomic distances that can be resolved are decreased in the same proportion. Importantly, FCC-hh and FCC-ee share the same ~100 km tunnel infrastructure. This paper focuses on the FCC-hh, summarising its key features, such as accelerator design, performance reach, and underlying technologies. The discussion is based on the 2019 conceptual design report (CDR) [1], which represents a study milestone, but also describes more recent design activities and indicates future directions.