Future Circular Collider
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).
The discovery of a "light" Higgs boson with a mass of 125 GeV revamped the discussion for a circular lepton collider[6] 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),[7][8] 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.
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.
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.
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: The LHC has inaugurated a new phase of detailed studies of the properties of the Higgs boson and the way in which it interacts with the other SM particles.
Future colliders with a higher energy and collision rate will largely contribute in performing these measurements, deepening our understanding of the Standard Model processes, test its limits and search for possible deviations or new phenomena that could provide hints for new physics.
Strategic R&D has been identified in the CDR[13] over the coming years will concentrate on minimising construction costs and energy consumption, whilst maximising the socio-economic impact with a focus on benefits for industry and training.
More specifically, high luminosity and improved handling of lepton beams would create the opportunity to measure the properties of the Z, W, Higgs, and top particles, as well as the strong interaction, with increased accuracy.
Moreover, measurements of invisible or exotic decays of the Higgs and Z bosons would offer discovery potential for dark matter or heavy neutrinos with masses below 70 GeV.
In effect, the FCC-ee could enable profound investigations of electroweak symmetry breaking and open a broad indirect search for new physics over several orders of magnitude in energy or couplings.
This makes a total of nearly 35 years for construction and operation of FCC-ee A future energy-frontier hadron collider will be able to discover force carriers of new interactions up to masses of around 30 TeV if they exist.
A hadron collider will also extend the study of Higgs and gauge boson interactions to energies well above the TeV scale, providing a way to analyse in detail the mechanism underlying the breaking of the electroweak symmetry.
The FCC-he collider would be both a high-precision Higgs factory[18] and a powerful microscope that could discover new particles, study quark/gluon interactions, and examine possible further substructure of matter in the world.
This could allow alternative technologies to be considered e.g. high-temperature superconducting magnets, and should lead to improved parameters and reduced implementation risks, compared to immediate construction after HL-LHC.
This machine could offer a first measurement of the Higgs self-coupling and directly produce particles at significant rates at scales up to 12 TeV – almost doubling the HL-LHC discovery reach for new physics.
[19] The foundations for these advancements are being laid in focused R&D programmes: Numerous other technologies from various fields (accelerator physics, high-field magnets, cryogenics, vacuum, civil engineering, material science, superconductors, ...) are needed for reliable, sustainable and efficient operation.
The beams that move in a circular accelerator lose a percentage of their energy due to synchrotron radiation: up to 5% every turn for electrons and positrons, much less for protons and heavy ions.
The future lepton and hadron colliders would make intensive use of low-temperature superconducting devices, operated at 4.5 K and 1.8 K, requiring very large-scale distribution, recovery, and storage of cryogenic fluids.
To protect the magnet cold bore from the head load, the vacuum system needs to be resistant against electron cloud effects, highly robust, and stable under superconducting quench conditions.
Moreover, fast self-adapting control systems with sub-millimeter collimation gaps are necessary to prevent irreversible damage of the machine and manage the 8.3 GJ stored in each beam.
To address these challenges, the FCC study searches for designs that can withstand the large energy loads with acceptable transient deformation and no permanent damage.
The Large Hadron Collider at CERN with its High Luminosity upgrade is the world's largest and most powerful particle accelerator and is expected to operate until 2036.
The ISC is responsible for the proper execution and implementation of the decisions of the ICB, deriving and formulating the strategic scope, individual goals and the work programme of the study.
[28] Physicist, author, content creator Sabine Hossenfelder[30] criticized a relevant promotional video for outlining a wide range of open problems in physics, despite the fact that the accelerator will likely only have the potential to resolve a small part of them.
[31][32] Research from experimental data on the cosmological constant, LIGO noise, and pulsar timing, suggests it's very unlikely that there are any new particles with masses much higher than those which can be found in the standard model or the LHC.
Gian Giudice, Head of CERN's Theoretical Physics Department wrote a paper on the "Future of High-Energy Colliders"[37] while other commentary came from Jeremy Bernstein, Lisa Randall, James Beacham,[38] Harry Cliff[39][40] and Tommaso Dorigo[41][42] among others.
In a recent interview theorist for the CERN Courier, Nima Arkani-Hamed described the concrete experimental goal for a post-LHC collider: "While there is absolutely no guarantee we will produce new particles, we will definitely stress test our existing laws in the most extreme environments we have ever probed.
