[Paper Review] Future Circular Lepton Collider FCC-ee: Overview and Status

I. Agapov, M. Benedikt+22 more|arXiv (Cornell University)|Jan 1, 2022

Particle Detector Development and Performance14 citations

TL;DR

The paper proposes the Future Circular Collider e+e− (FCC-ee) as a high-luminosity Higgs and electroweak factory, operating at four center-of-mass energies (91, 160, 240, and 365 GeV) with luminosities up to 2×10³⁶ cm⁻²s⁻¹ per interaction point. It achieves unprecedented precision in electroweak measurements and serves as a stepping stone toward a 100 TeV hadron collider (FCC-hh), leveraging shared infrastructure and advanced technologies for energy efficiency and sustainability.

ABSTRACT

The worldwide High Energy Physics community widely agrees that the next collider should be a Higgs factory. Acknowledging this priority, in 2021 CERN has launched the international Future Circular Collider (FCC) Feasibility Study (FS). The FCC Integrated Project foresees, in a first stage, a high-luminosity high-energy electron-positron collider, serving as Higgs, top and electroweak factory, and, in a second stage, an energy frontier hadron collider, with a centre-of-mass energy of at least 100 TeV. In this paper, we address a few key elements of the FCC-ee accelerator design, its performance reach, and underlying technologies, as requested by the Snowmass process. The Conceptual Design Report for the FCC, published in 2019, serves as our primary reference. We also summarize a few recent changes and improvements.

Motivation & Objective

• . The paper aims to present the current status and design optimization of the FCC-ee, a proposed e+e− collider as the first stage of the Future Circular Collider (FCC) project.
• It addresses the need for a next-generation Higgs factory to resolve outstanding questions in electroweak physics and top quark properties.
• The study evaluates FCC-ee's performance, energy efficiency, and technological feasibility in the context of the global particle physics roadmap.
• It explores synergies with existing and future facilities, including the LHC, EIC, CEPC, and advanced light sources, to maximize scientific return and technological spillover.
• The objective includes assessing the feasibility of future upgrades, such as ERL and muon collider concepts, for extending FCC-ee's physics reach.

Proposed method

• . The FCC-ee design is based on a 91.2 km circumference ring with 8 surface sites, optimized for reduced risk and enhanced operational flexibility.
• It employs superconducting RF cavities and high-field magnets to achieve luminosities up to 2×10³⁶ cm⁻²s⁻¹ per interaction point at the Z pole.
• The collider operates at four distinct center-of-mass energies: 91 GeV (Z resonance), 160 GeV (WW threshold), 240 GeV (ZH peak), and 365 GeV (t¯t threshold), enabling precision measurements.
• Resonant depolarization techniques allow energy calibration with sub-MeV precision (100 keV for mZ, 300 keV for mW).
• The design reuses CERN’s existing injector complex (Linac4 → PSB → PS → SPS → LHC) and shares civil engineering and technical infrastructure with the subsequent FCC-hh hadron collider.
• Energy efficiency is achieved through advanced cryogenics, HTS cables, and energy recovery systems, with estimated power consumption of ~300 MW at peak operation.

Experimental results

Research questions

• RQ1 . What is the optimal design and performance reach of FCC-ee as a Higgs and electroweak factory, and how does it compare to other proposed lepton colliders?
• RQ2 How can FCC-ee achieve high luminosity while maintaining energy efficiency and sustainability over its 15-year physics program?
• RQ3 What are the technical and financial feasibility aspects of transitioning from FCC-ee to the FCC-hh 100 TeV hadron collider?
• RQ4 What synergies exist between FCC-ee and existing or future facilities such as the LHC, EIC, CEPC, and synchrotron light sources?
• RQ5 What upgrade paths—such as ERL or muon collider—could extend the physics reach of FCC-ee beyond its baseline operation?

Key findings

• . FCC-ee achieves a peak luminosity of 2×10³⁶ cm⁻²s⁻¹ per interaction point at the Z pole, with a total integrated luminosity of 48 ab⁻¹/year for two interaction points.
• At the t¯t threshold (365 GeV), the luminosity is 1.3×10³⁴ cm⁻²s⁻¹ per IP, with a total of 0.34 ab⁻¹/year for two points.
• The collider operates with an electrical power consumption of ~259–354 MW, depending on center-of-mass energy, and is projected to consume only ~2.5 times the energy of LEP despite 10⁵× higher luminosity.
• The design is the most energy-efficient Higgs factory proposal, with the lowest energy consumption per unit of integrated luminosity across the 90–365 GeV range.
• The FCC-ee design enables sub-MeV energy calibration (100 keV for mZ) via resonant depolarization, crucial for precision electroweak measurements.
• The project is compatible with future upgrades, including a transition to FCC-hh at 100 TeV, and potential ERL or muon collider concepts, though these remain under study.