The Future Circular Collider (FCC) is a proposed particle accelerator with an energy significantly above that of previous circular colliders, such as the Super Proton Synchrotron, the Tevatron, and the Large Hadron Collider (LHC). The FCC project is considering three scenarios for collision types: FCC-hh, for hadron-hadron collisions, including proton-proton and heavy ion collisions, FCC-ee, for electron-positron collisions, and FCC-eh, for electron-hadron collisions. In FCC-hh, each beam would have a total energy of 560 MJ. With a centre-of-mass collision energy of 100 TeV (vs 14 TeV at LHC) the total energy value increases to 16.7 GJ. These total energy values exceed the present LHC by nearly a factor of 30. CERN hosted an FCC study exploring the feasibility of different particle collider scenarios with the aim of significantly increasing the energy and luminosity compared to existing colliders. It aims to complement existing technical designs for proposed linear electron/positron colliders such as the International Linear Collider and the Compact Linear Collider. The study explores the potential of hadron and lepton circular colliders, performing an analysis of infrastructure and operation concepts and considering the technology research and development programmes that are required to build and operate a future circular collider. A conceptual design report was published in early 2019, in time for a scheduled update of the European Strategy for Particle Physics.
Background The CERN study was initiated as a direct response to the high-priority recommendation of the updated European Strategy for Particle Physics, published in 2013 which asked that "CERN should undertake design studies for accelerator projects in a global context, with emphasis on proton-proton and electron-positron high-energy frontier machines. These design studies should be coupled to a vigorous accelerator R&D programme, including high-field magnets and high-gradient accelerating structures, in collaboration with national institutes, laboratories and universities worldwide". The goal was to inform the next Update of the European Strategy for Particle Physics (2019–2020) and the wider physics community for the feasibility of circular colliders complementing previous studies for linear colliders as well as other proposal for particle physics experiments. The launch of the FCC study was also in line with the recommendations of the United States' Particle Physics Project Prioritization Panel (P5) and of the International Committee for Future Accelerators (ICFA), a working group of the International Union of Pure and Applied Physics. The discovery of the Higgs boson at the LHC, together with the absence so far of any phenomena beyond the Standard Model in collisions at centre of mass energies up to 8 TeV, has triggered an interest in future circular colliders to push the energy and precision frontiers complementing studies for future linear machines. The discovery of a "light" Higgs boson with a mass of 125 GeV revamped the discussion for a circular lepton collider that would allow detailed studies and precise measurement of this new particle. With the study of a new 80–100 km circumference tunnel (see also VLHC), that would fit in the Geneva region, it was realized that a future circular lepton collider could offer collision energies up to 400 GeV (thus allowing for the production of top quarks) at unprecedented luminosities. The design of FCC-ee (formerly known as TLEP (Triple-Large Electron-Positron Collider)) was combining the experience gained by LEP2 and the latest B-factories. Two main limitations to circular-accelerator performance are energy loss due to synchrotron radiation, and the maximum value of magnetic fields that can be obtained in bending magnets to keep the energetic beams in a circular trajectory. Synchrotron radiation is of particular importance in the design and optimization of a circular lepton collider and limits the maximum energy that can be reached as the phenomenon depends on the mass of the accelerated particle. To address these issues a sophisticated machine design along with the advancement of technologies like accelerating (RF) cavities and high-field magnets are needed. Future "intensity and luminosity frontier" lepton colliders like those considered by the FCC study would enable the study with very high precision of the properties of the Higgs boson, the W and Z bosons and the top quark, pinning down their interactions with an accuracy at least an order of magnitude better than today. The FCC-ee could collect 1012 Z bosons, 108 W pairs, 106 Higgs bosons and 4 · 105 top-quark pairs per year. As a second step, an "energy frontier" collider at 100 TeV (FCC-hh) could be a "discovery machine" offering an eightfold increase compared to the current energy reach of the LHC. The FCC integrated project, combining FCC-ee and FCC-hh, would rely on a shared and cost effective technical and organizational infrastructure, as was the case with LEP followed by LHC. This approach improves by several orders the sensitivity to elusive phenomena at low mass and by an order of magnitude the discovery reach for new particles at the highest masses. This will allow to uniquely map the properties of the Higgs boson and electroweak sector and broaden the exploration for different dark matter candidate particles complementing other approaches with neutrino beams, non-collider experiments and astrophysics experiments.
Motivation The LHC has advanced the science of matter and the Standard Model (SM). The discovery of the Higgs boson completed the particle-related component of the Standard Model of Particle Physics, the theory that describes the laws governing most of the known Universe. Yet the Standard Model cannot explain several observations, such as:
… excerpt ends here. Continue reading the full article.
