European Strategy Group recommends FCC-ee

The European Strategy Group (ESG) has finalised its recommendations for the 2026 update to the European Strategy for Particle Physics. As required by the CERN Council, the recommendations include a preferred option for the next large-scale collider at CERN and a prioritised alternative option to be pursued if the preferred plan turns out not to be feasible or competitive.

“The electron–positron Future Circular Collider (FCC-ee) is recommended as the preferred option for the next flagship collider at CERN,” explains strategy secretary Karl Jakobs of the University of Freiburg. “A descoped FCC-ee is the preferred alternative option. Descoping scenarios include removing the top-quark run, constructing two rather than four interaction regions and experiments, and decreasing the RF-system power.”

The ESG drafted its recommendations in a dedicated meeting at Monte Verità in Ascona, Switzerland. From 1 to 5 December, 62 delegates from across the field built on community inputs and the work of the Physics Preparatory Group to elaborate a proposal for the update to the European Strategy for Particle Physics. The recommendations address a broad range of topics and goals related to research in high-energy physics in Europe and beyond (CERN Courier November/December 2025 p23).

Seven large-scale collider projects have been the subject of a comparative assessment: CLIC, FCC-ee, FCC-hh, LCF, LEP3, LHeC and a muon collider (see “Seven colliders for CERN”). Following community submissions to the strategy process in March 2025 and at the open symposium in Venice in June 2025, a consensus emerged that an electron–positron Higgs and electroweak factory is the optimal collider to follow the High-Luminosity LHC (HL-LHC), with FCC-ee the favoured machine of a strong majority of the community (CERN Courier September/October 2025 p24). The identification of a descoped FCC-ee as the preferred alternative option was a new development in Ascona.

“Descoping would reduce the construction cost of FCC-ee by approximately 15%,” says Jakobs. “Although this would have a significant impact on the breadth of the physics programme and the precision achieved, the descoped FCC-ee would still provide a very strong physics programme and a viable path towards high energies, compared to the alternative collider options. Should additional resources become available, these descoping scenarios would be reversible.”

“The other electron-positron collider options offer substantially reduced precision physics programmes and would not be competitive with a collider like the FCC-ee,” continues Jakobs. “Moreover, in themselves, they currently lack a viable path towards energies of 10 TeV.”

The FCC-ee would maintain European leadership in high-energy particle physics

In preparation for the Ascona meeting, working groups were set up to study national inputs, the physics and technology of the large-scale flagship collider projects, the implementation of the strategy, relations with other fields of physics, sustainability and environmental impact, public engagement, education and communication, as well as social and career aspects, and knowledge and technology transfer.

According to the ESG, the FCC-ee would deliver the world’s broadest high-precision particle-physics programme, with an outstanding discovery potential through the Higgs, electroweak, flavour and top-quark sectors, as well as advances in QCD. Its technical feasibility, scope and cost are defined by the FCC Feasibility Study (CERN Courier May/June 2025 p9). The FCC-ee would maintain European leadership in high-energy particle physics, says the ESG, as well as advancing technology and providing significant societal benefits.

“The FCC-ee or the descoped version would also pave the way towards a hadron collider reusing the tunnel and much of the infrastructure, providing direct discovery reach well beyond the 10 TeV parton energy scale, in line with the community’s ambition for exploration at the highest achievable energy,” concludes Jakobs. “The overwhelming endorsement of the FCC-ee by the particle-physics communities of CERN’s Member and Associate Member States further reinforces it as the preferred path.”

The recommendations of the ESG advise but do not constrain the CERN Council, which is expected to formally deliberate on the official update to the European Strategy for Particle Physics at a dedicated Council Session in Budapest in May 2026.