The final report of a detailed study investigating the technical and financial feasibility of a Future Circular Collider (FCC) at CERN was released on 31 March. Building on a conceptual design study conducted between 2014 and 2018, the three-volume report is authored by over 1400 scientists and engineers in more than 400 institutes worldwide, and covers aspects of the project ranging from civil engineering to socioeconomic impact. As recommended in the 2020 update to the European Strategy for Particle Physics (ESPP), it was completed in time to serve as an input to the ongoing 2026 update to the ESPP (see “European strategy update: the community speaks“).
The FCC is a proposed collider infrastructure that could succeed the LHC in the 2040s. Its scientific motivation stems from the discovery in 2012 of the final particle of the Standard Model (SM), the Higgs boson, with a mass of just 125 GeV, and the wealth of precision measurements and exploratory searches during 15 years of LHC operations that have excluded many signatures of new physics at the TeV scale. The report argues that the FCC is particularly well equipped to study the Higgs and associated electroweak sectors in detail and that it provides a broad and powerful exploratory tool that would push the limits of the unknown as far as possible.
The report describes how the FCC will seek to address key domains formulated in the 2013 and 2020 ESPP updates, including: mapping the properties of the Higgs and electroweak gauge bosons with accuracies orders of magnitude better than today to probe the processes that led to the emergence of the Brout–Englert–Higgs field’s nonzero vacuum expectation value; ensuring a comprehensive and accurate campaign of precision electroweak, quantum chromodynamics, flavour and top-quark measurements sensitive to tiny deviations from the SM, probing energy scales far beyond the direct kinematic reach; improving by orders of magnitude the sensitivity to rare and elusive phenomena at low energies, including the possible discovery of light particles with very small couplings such as those relevant to the search for dark matter; and increasing by at least an order of magnitude the direct discovery reach for new particles at the energy frontier.
This technology has significant potential for industrial and societal applications
The FCC research programme outlines two possible stages: an electron–positron collider (FCC-ee) running at several centre-of-mass energies to serve as a Higgs, electroweak and top-quark factory, followed at a later stage by a proton–proton collider (FCC-hh) operating at an unprecedented collision energy. An FCC-ee with four detectors is judged to be “the electroweak, Higgs and top factory project with the highest luminosity proposed to date”, able to produce 6 × 1012 Z bosons, 2.4 × 108 W pairs, almost 3 × 106 Higgs bosons, and 2 × 106 top-quark pairs over 15 years of operations. Its versatile RF system would enable flexibility in the running sequence, states the report, allowing experimenters to move between physics programmes and scan through energies at ease. The report also outlines how the FCC-ee injector offers opportunities for other branches of science, including the production of spatially coherent photon beams with a brightness several orders of magnitude higher than any existing or planned light source.
The estimated cost of the construction of the FCC-ee is CHF 15.3 billion. This investment, which would be distributed over a period of about 15 years starting from the early 2030s, includes civil engineering, technical infrastructure, electron and positron accelerators, and four detectors.
Ready for construction
The report describes how key FCC-ee design approaches, such as a double-ring layout, top-up injection with a full-energy booster, a crab-waist collision scheme, and precise energy calibration, have been demonstrated at several previous or presently operating colliders. The FCC-ee is thus “technically ready for construction” and is projected to deliver four-to-five orders of magnitude higher luminosity per unit electrical power than LEP. During operation, its energy consumption is estimated to vary
from 1.1 to 1.8 TWh/y depending on the operation mode compared to CERN’s current consumption of about 1.3 TWh/y. Decarbonised energy including an ever-growing contribution from renewable sources would be the main source of energy for the FCC. Ongoing technology R&D aims at further increasing FCC-ee’s energy efficiency (see “Powering into the future”).
Assuming 14 T Nb3Sn magnet technology as a baseline design, a subsequent hadron collider with a centre-of-mass energy of 85 TeV entering operation in the early 2070s would extend the energy frontier by a factor six and provide an integrated luminosity five to 10 times higher than that of the HL-LHC during 25 years of operation. With four detectors, FCC-hh would increase the mass reach of direct searches for new particles to several tens of TeV, probing a broad spectrum of beyond-the-SM theories and potentially identifying the sources of any deviations found in precision measurements at FCC-ee, especially those involving the Higgs boson. An estimated sample of more than 20 billion Higgs bosons would allow the absolute determination of its couplings to muons, to photons, to the top quark and to Zγ below the percent level, while di-Higgs production would bring the uncertainty on the Higgs self-coupling below the 5% level. FCC-hh would also significantly advance understanding of the hot QCD medium by enabling lead–lead and other heavy-ion collisions at unprecedented energies, and could be configured to provide electron–proton and electron–ion collisions, says the report.
The FCC-hh design is based on LHC experience and would leverage a substantial amount of the technical infrastructure built for the first FCC stage. Two hadron injector options are under study involving a superconducting machine in either the LHC or SPS tunnel. For the purpose of a technical feasibility analysis, a reference scenario based on 14 T Nb3Sn magnets cooled to 1.9 K was considered, yielding 2.4 MW of synchrotron radiation and a power consumption of 360 MW or 2.3 TWh/y – a comparable power consumption to FCC-ee.
FCC-hh’s power consumption might be reduced below 300 MW if the magnet temperature can be raised to 4.5 K. Outlining the potential use of high-
temperature superconductors for 14 to 20 T dipole magnets operating at temperatures between 4.5 K and 20 K, the report notes that such technology could either extend the centre-of-mass energy of FCC-hh to 120 TeV or lead to significantly improved operational sustainability at the same collision energy. “The time window of more than 25 years opened by the lepton-collider stage is long enough to bring that technology to market maturity,” says FCC study leader Michael Benedikt (CERN). “High-temperature superconductors have significant potential for industrial and societal applications, and particle accelerators can serve as pilots for market uptake, as was the case with the Tevatron and the LHC for NbTi technology.”
Society and sustainability
The report details the concepts and paths to keep the FCC’s environmental footprint low while boosting new technologies to benefit society and developing territorial synergies such as energy reuse. The civil construction process for FCC-ee, which would also serve FCC-hh, is estimated to result in about 500,000 tCO2(eq) over a period of 10 years, which the authors say corresponds to approximately one-third of the carbon budget of the Paris Olympic Games. A socio-economic impact assessment of the FCC integrating environmental aspects throughout its entire lifecycle reveals a positive cost–benefit ratio, even under conservative assumptions and adverse implementation conditions.
The actual journey towards the realisation of the FCC starts now
A major achievement of the FCC feasibility study has been the development of the layout and placement of the collider ring and related infrastructure, which have been optimised for scientific benefit while taking into account territorial compatibility, environmental and construction constraints, and cost. No fewer than 100 scenarios were developed and analysed before settling on the preferred option: a ring circumference of 90.7 km with shaft depths ranging between 200 and 400 m, with eight surface sites and four experiments. Throughout the study, CERN has been accompanied by its host states, France and Switzerland, working with entities at the local, regional and national levels to ensure a constructive dialogue with territorial stakeholders.
The final report of the FCC feasibility study together with numerous referenced technical documents have been submitted to the ongoing ESPP 2026 update, along with studies of alternative projects proposed by the community. The CERN Council may take a decision around 2028.
“After four years of effort, perseverance and creativity, the FCC feasibility study was concluded on 31 March 2025,” says Benedikt. “The actual journey towards the realisation of the FCC starts now and promises to be at least as fascinating as the successive steps that brought us to the present state.”
