Accelerators | Future Circular Collider

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The proposed FCC integrated programme, foresees a new 91-km-long circular tunnel in the Franco-Swiss region around CERN that could house a new research infrastructure for particle physics.

The new tunnel would initially host an electron–positron collider (FCC-ee) allowing precise measurement of the properties of the Higgs boson and other Standard Model particles. The second step, would be an energy frontier proton collider (FCC-hh), offering collision energies of 100 TeV or higher (i.e. 8 times the energy of the LHC) following developments in the superconducting and magnet technologies.

The FCC project will validate the key performance enablers at particle accelerators in a sustainable way while offering opportunities for co-development with industry of advanced technologies for applications beyond high-energy physics in line with the tradition of previous Big Science projects.

The FCC collaboration, with the support of the Horizon 2020 EU-funded FCCIS project, have launched a Feasibility Study to support the development of a roadmap for the design and the implementation plan of a new research infrastructure to efficiently explore both frontiers by the end of the 21st century.

FCC-ee
FCC-hh
FCC-int

The intensity frontier lepton collider

The proposed circular lepton collider (FCC-ee) is a highest-luminosity Higgs and electroweak factory energy-frontier electron-positron collider (FCC-ee) spanning the energies from 80 to 400 GeV. The clean environment of a circular lepton collider will allow to study with high precision the Z, W, Higgs and top particles, with samples of trillions (5·10¹²) Z bosons, 10⁸ W pairs and millions (10⁶) Higgs bosons and top quark pairs. The rich menu of the FCC-ee physics possibilities combines a set of precision measurements, feebly-coupled particle sensitivity, and rare process studies, which will challenge and shape particle physics for many decades

Several experimental facts require extension of the Standard Model, in particular: the dominance of matter over antimatter in the Universe; the evidence for dark matter from astronomical and cosmological observations; and, more closely to particle physics, the smallness of the neutrino masses, about 10⁻⁷ times smaller than that of the electron. The possible solutions to these questions seem to require the existence of new particles or phenomena that can occur over an immense range of mass scales and coupling strengths. The discovery of new particles, before their actual observation, has often been guided in the past by predictions based a long history of experiments and of theory maturation. In this context, a decisive improvement on the precision of certain electroweak precision observables, combined with other precision measurements of the properties of the Higgs boson, the top quark, the tau lepton and hadrons containing the charm and beauty quarks, could play a crucial role, by integrating sensitivity to a large range of new physics possibilities. The clean environment and the high luminosities of the FCC-ee will offer unprecedented sensitivity to signs of new physics that could have the form of small deviations from the Standard Model, of forbidden decay processes or of production of new particles with very small couplings.

Each key ‘ingredient’ of the FCC-ee has already been demonstrated at one or several previous colliders or test facilities. Such proven ingredients include, for example, the vertical spot size and the transverse emittances of the beams, the synchrotron-radiation photon energies, and synchrotron-radiation power per unit length, the bunch charge, the ‘crab-waist’ collision scheme, the radiofrequency system and the positron production rate. One of the great advantages of the circular lepton colliders, like FCC-ee, is the possibility of serving several interaction points with a net overall gain both in integrated luminosity and luminosity per power consumption unit.
FCC-hh: The energy-frontier hadron collider

The FCC-hh focuses on a 100 TeV hadron collider, with an integrated luminosity at least a factor of 5 larger than what will be achieved in the lifetime of the LHC. Its unprecedented centre of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries. The FCC-hh will extend the current energy frontier by almost an order of magnitude, offering the potential for direct exploration of the multi-TeV region. This will enable the Higgs self-coupling precisely and thoroughly explore the dynamics of electroweak symmetry breaking at the TeV scale, to elucidate the nature of the electroweak phase transition. Moreover, the interplay between the FCC-ee and FCC-hh stages is essential for a broad spectrum of unique Higgs measurements. FCC-hh will also give us a definitive answer about the WIMPs paradigm as thermal dark matter candidates will either be discovered, or ruled out. Finally, also based on the lessons from FCC-ee, it could give us access to new particles whose existence could be indirectly predicted by precision measurements during the earlier FCC-ee phase.

The layout of the FCC-hh has been developed to be consistent with the FCC-ee layout as well as allowing smooth integration with CERN's existing accelerator complex. Moreover, it could host up to 4 experiments as is currently the case in LHC.

The timescale means that FCC-hh technologies can be brought to the required technology readiness level, improving their performance and allowing for sustainable large-scale production, through a dedicated R&D programme.

One of the key technologies for an energy-frontier colliders is high-field magnets, and the underlying superconductor. The ongoing High-Luminosity upgrade of the LHC (HL-LHC) represents an important milestone in that direction, including a few tens of magnets with a peak magnetic field of 11–12 T. For the FCC-hh, various configurations of 16 T and novel superconducting materials are currently being tested along with options for High-Temperature superconductors. Another key technology, is an energy-efficient cryogenic refrigeration infrastructure based on novel coolants along with a high-reliability distribution system. Finally, the optimisation of high-power beam transfer and local magnet energy recovery are among the technologies that would improve the performance and find applications beyond particle physics.

As a single project, FCC-hh will serve the global physics community for about 25 years. Combined with a lepton collider (FCC-ee), as a first step in the same tunnel, it would provide a global, multi-decade research programme until the end of the 21st century.

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FCC Integrated Programme

The most effective and comprehensive approach to thoroughly explore the open questions in modern particle physics is a staged research programme, integrating in sequence lepton (FCC-ee) and hadron (FCC-hh) collision programmes, to achieve an exhaustive understanding of the Standard Model and of electroweak symmetry breaking, and to maximise the potential for the discovery of phenomena beyond the Standard Model.

The FCC positions itself as the most powerful heir of the future LHC Higgs’ legacy. On one hand it will extend the range of measurable Higgs properties allowing more incisive and model independent determinations of its couplings with other particles. On the other hand, the combination of superior precision and energy reach provides a framework in which indirect and direct probes of new physics complement each other, and cooperate to characterise the nature of possible discoveries. In addition, the new research infrastructure would offer a number of other physics opportunities based on heavy-ion collisions and electron-proton scattering (FCC-eh) that are unattainable at linear-collider facilities.

The staged approach of the FCC-integrated project creates a new window in time in which to develop the advanced technologies needed to build a longterm cost- and energy-efficient highest energy hadron collider. This integrated project leverages CERN’s existing machine complex, notably the HL-LHC, its infrastructures and pre-accelerators in the best way. They can serve as injectors for both FCC-ee and FCC-hh. The combination of available infrastructure and organisational and administrative services suitable for large-scale technology research projects is the key to the successful implementation of a large-scale project.

As was the case with LEP followed by LHC, this approach permits the control of technical and financial risks without self-imposed constraints. It cements and enlarges Europe’s leadership in particle and high energy physics for decades to come.

Finally, the new research infrastructure serving a worldwide community, tightly involving industrial partners and providing training at all education levels over multiple decades, would deliver the highest socio-economic impact.

Timeplan

The Integrated FCC Project offers a research program spanning more than 70 years, until the end of the 21st century.