FCC-ee

FCC-ee
Name	Future Circular Collider (electron–positron)
Caption	Conceptual layout for a circular electron–positron collider in a large tunnel
Location	Europe
Status	Proposed
Proposed	2019
Type	Particle collider
Energy	Up to ~365 GeV centre-of-mass
Circumference	~91 km (baseline studies)
Operators	CERN (proposal origin)

FCC-ee.

Overview

The project is a proposed high-luminosity circular electron–positron collider designed as a precision machine to probe the Standard Model and search for indirect signs of new physics. It is envisaged as a successor to the Large Electron–Positron Collider and a potential first stage in a staged programme culminating in a high-energy hadron machine analogous to the vision for the Future Circular Collider (hadron) concept. Design studies have been coordinated by teams associated with CERN, national laboratories such as DESY, KEK, and SLAC National Accelerator Laboratory, and numerous university groups across Europe and beyond.

Science goals and physics program

The physics programme emphasises high-precision measurements of the Higgs boson, Z boson, W boson, and top quark properties to test electroweak radiative corrections and constrain extensions such as supersymmetry, composite Higgs models, and theories with dark matter candidates. Key targets include percent-to-per-mille determinations of the Higgs boson couplings, model-independent extractions of the total Higgs width, and threshold scans for the top quark mass and Yukawa coupling. Precision electroweak observables from Z-pole and WW runs aim to improve constraints on parameters used in global fits such as those performed by collaborations linked to the Global Electroweak Fit community and groups around the Particle Data Group. Searches for rare and forbidden decays complement direct searches undertaken at facilities like the Large Hadron Collider and proposed projects such as the International Linear Collider and Compact Linear Collider.

Accelerator design and technology

The machine concept uses a novel large circular tunnel to achieve high luminosity at center-of-mass energies ranging from the Z pole through the Higgs factory regime to top-pair threshold. Key accelerator technologies include strong focusing final‑focus systems developed with experience from the Large Hadron Collider injector chain, high-efficiency superconducting radio-frequency cavities similar to those used at European XFEL and CEBAF, top-up injection schemes inspired by synchrotron light sources such as ESRF and APS, and advanced beam instrumentation drawing on expertise from CERN accelerator divisions and institutes like Budker Institute of Nuclear Physics. Beam dynamics challenges include mitigation of beamstrahlung effects, collective instabilities studied in the context of LEP operations, and novel crab-waist collision schemes demonstrated at flavor factories like KEKB. The overall lattice and optics designs build upon work from the International Committee for Future Accelerators reports and technical inputs from national accelerator laboratories.

Detector concepts and experiments

Detector concepts proposed for the project leverage silicon vertexing, high-granularity calorimetry, and precision tracking systems developed for experiments such as ATLAS, CMS, and the ILC detector concepts. Multiple interaction regions with complementary detectors have been studied to cover precision electroweak, Higgs, and flavor physics programmes; collaborations of universities and institutes from the CERN Member and Associate Member states, along with groups from United States Department of Energy laboratories and Japanese institutions, contribute to conceptual design reports. Advanced particle-flow reconstruction techniques build on developments from ALEPH and modern machine-learning toolchains employed by teams affiliated with the European Laboratory for Particle Physics community.

Site, infrastructure, and timeline

Baseline studies have considered a tunnel circumference around major existing accelerator sites in Europe, connecting to regional infrastructure and transport networks serving cities that host laboratories like Geneva and institutes with prior accelerator heritage such as Orsay. Civil engineering assessments reference precedent projects including the construction of the Large Hadron Collider tunnel and large-scale tunnelling works in the Alps. The staged deployment strategy envisions preparatory site studies, environmental impact assessments, and technology testbeds before construction, with a timeline that depends on international commitment and follows strategic roadmaps similar to those set by the European Strategy for Particle Physics process. Synergies with regional grid power providers, cryogenic suppliers, and industrial partners experienced from projects like ITER are central to infrastructure planning.

Governance, collaboration, and funding

Governance frameworks proposed mirror large international science collaborations coordinated through intergovernmental and institutional agreements involving CERN, national funding agencies such as the European Research Council funders, ministries of science and technology from Member States, and multinational consortia of laboratories including DESY and Rutherford Appleton Laboratory. Funding scenarios explore contributions from state actors and in-kind contributions from industrial partners with experience in accelerator construction, echoing models used for LHC and multi-national projects like XFEL. Collaboration structures emphasize open technical review by working groups formed under the guidance of advisory bodies such as the International Advisory Committee and seek alignment with global priorities articulated by the Particle Physics Community Planning exercises.

Category:Particle accelerators Category:Proposed particle physics facilities