Future Colliders Comparative Evaluation -- Working Group Report

TL;DR

This report provides a structured, cross-project comparison of future collider concepts intended to succeed HL-LHC, focusing on FCC-ee, FCC-hh, CLIC, LCF, FCChh, Muon Collider, and parallel options such as CEPC and ILC. It uses a shared set of criteria—performance, environment, readiness, cost, human resources, timelines, and operating requirements—to evaluate maturity, sustainability, and feasibility within the 2045–2050 operational window. The analysis finds that the FCC integrated programme offers a coherent, long-term pathway but recognizes substantial RD, cost, and siting considerations for each alternative, with muon and wakefield-based concepts remaining challenging to mature within the strategy timeframe. The report emphasizes realism in scheduling, the need for phased decisions between 2028 and 2030, and the importance of reusing and coordinating CERN's existing infrastructure and regional RD programs. Overall, it highlights that sustainability, resource constraints, and technology readiness will shape the selection of the next flagship facility and its upgrade path, while remaining open to distant, high-risk options that could transform the field if matured.

Abstract

In anticipation of the completion of the High-Luminosity Large Hadron Collider (HL-LHC) programme by the end of 2041, CERN is preparing to launch a new major facility in the mid-2040s. According to the 2020 European Strategy for Particle Physics (ESPP), the highest-priority next collider is an electron-positron Higgs factory, followed in the longer term by a hadron-hadron collider at the highest achievable energy. The CERN directorate established a Future Colliders Comparative Evaluation working group in June 2023. This group brings together project leaders and domain experts to conduct a consistent evaluation of the Future Circular Collider (FCC) and alternative scenarios based on shared assumptions and standardized criteria. This report presents a comparative evaluation of proposed future collider projects submitted as input for the Update of the European Strategy for Particle Physics. These proposals are compared considering main performance parameters, environmental impact and sustainability, technical maturity, cost of construction and operation, required human resources, and realistic implementation timelines. An overview of the international collider projects within a similar timeframe, notably the CEPC in China and the ILC in Japan is also presented, as well as a short review of the status and prospects of new accelerator techniques.

Figures (10)

• Figure 1.1: Integrated luminosity over all experiments per year of nominal operation, per unit of electricity consumption for future electron-positron colliders (excluding off-line computing) --- see Tables \ref{['tab:Parameters_CLIC_FCC_LCF']}, \ref{['tab:Param_CLIC_LCF_upgrades']} and \ref{['tab:Parameters_ILC_CEPC_rescaled']}; the performance has been rescaled to the fccee operational year for cepc and to lcf 250 lp for the ilc (see Table \ref{['tab:operational_year']}). For lc the total luminosity (including that below 99 % of the nominal com energy) is considered. lep and lep2 data were respectively taken for the years 1993 and 2000 bib:Assmann_LEP2bib:electricity_LEP_1993bib:electricity_LEP2_2000. For the ilc, a single ip is considered but with two experiments (in "push-pull" mode, see Section \ref{['sec:ILC_intro']}). The information for lep3 has not been added at this stage.
• Figure 4.1: Conceptual layout of the clic collider (380).
• Figure 4.2: Schematic diagram of the fccee collider.
• Figure 4.3: Conceptual layout of the lcf/ilc collider.
• Figure 6.1: Schematic diagram of the fcchh collider.