[Paper Review] Report of the Snowmass 2021 e$^+$e$^-$-Collider Forum

M. Chamizo Llatas, Sridhara Dasu+4 more|arXiv (Cornell University)|Sep 7, 2022

Scientific Computing and Data Management4 citations

TL;DR

This Snowmass 2021 report evaluates electron-positron collider options for advancing precision Higgs and electroweak physics, with a focus on near-term Higgs factories (ILC, FCC-ee, CEPC) and long-term upgrades to 10 TeV energy scales. It advocates for early US participation in construction and R&D, emphasizing ILC’s early start advantage, C³ and WFA/ERL concepts for future cost and performance gains, and urgent detector R&D to enable full-scale e⁺e⁻ collider physics by the end of the decade.

ABSTRACT

A summary of the Snowmass 2021 e$^+$e$^-$-Collider Forum discussions, white papers submitted to the Snowmass 2021 community study, submissions of the Energy Frontier (EF) subgroups and the Accelerator Frontier (AF) Integrated Task Force (ITF) are presented.

Motivation & Objective

• To assess the scientific potential and technical feasibility of electron-positron colliders spanning from precision electroweak physics to the Energy Frontier.
• To compare linear (ILC, C³) and circular (FCC-ee, CEPC) collider designs in terms of cost, timeline, luminosity, and physics reach.
• To identify critical R&D needs in detectors, accelerators, and synergy with existing accelerator infrastructure to enable timely construction and physics output.
• To advocate for US leadership in R&D and potential construction of a future e⁺e⁻ collider, particularly through early investment in ILC and C³.
• To ensure detector readiness by the time the HL-LHC concludes, with a focus on precision timing, low-material tracking, and scalable systems.

Proposed method

• Evaluates linear and circular collider designs (ILC, FCC-ee, CEPC, CLIC, C³, CERC, ReLiC, ERLC) based on technical maturity, cost, power consumption, and upgrade paths.
• Compares physics reach across energy scales: Z/WW/threshold runs (≤1 TeV), Higgs self-coupling and top Yukawa access (1–3 TeV), and 10 TeV-scale discovery potential.
• Analyzes luminosity and integrated data requirements (e.g., 2 ab⁻¹ for ILC, 5 ab⁻¹ for FCC-ee at 250 GeV) to achieve sub-percent precision on Higgs couplings.
• Assesses polarization capabilities (especially in linear colliders) to enhance sensitivity to couplings and new physics.
• Evaluates advanced accelerator concepts like C³ (high-gradient, low-power), WFA (wakefield acceleration), and ERL (energy recovery) for future high-energy, high-luminosity operation.
• Proposes a staged detector R&D program focused on precision timing, material reduction in trackers, calorimeter performance, and scalable powering/cooling systems.

Experimental results

Research questions

• RQ1 Which e⁺e⁻ collider design offers the earliest start for precision Higgs and electroweak physics while ensuring long-term upgrade potential?
• RQ2 How can detector R&D be accelerated to ensure readiness for a full-scale e⁺e⁻ collider by the end of the HL-LHC era?
• RQ3 What are the cost, power, and timeline trade-offs between linear and circular collider paths to the 10 TeV Energy Frontier?
• RQ4 Can new accelerator technologies like C³, WFA, or ERL significantly reduce cost and power consumption while enabling high-luminosity operation?
• RQ5 What role should the US play in R&D and potential construction of a future e⁺e⁻ collider, especially given the global nature of the project?

Key findings

• The ILC offers the earliest physics start (within 12 years) due to mature technology and an established site, though it requires 11 years to collect 2 ab⁻¹ at 250 GeV compared to FCC-ee’s 3-year 5 ab⁻¹ run.
• FCC-ee and CEPC can achieve higher luminosity and faster data collection but require significantly more civil engineering, increasing cost and timeline by 13–18 years.
• C³ is the only newer proposal with a feasible timeline for early physics, though it requires a pre-construction demonstrator to validate its high-gradient, low-power design.
• Energy recovery linacs (CERC, ReLiC, ERLC) and WFA-based machines offer potential for 10 TeV-scale operation but require >25 years of R&D and are not viable before 2050.
• Detector R&D must prioritize precision timing, ultra-low material budget in trackers, and scalable cooling and powering systems to meet the demands of high-luminosity e⁺e⁻ collisions.
• The US should pursue R&D on multiple e⁺e⁻ collider options now to ensure technical readiness and global leadership, with Fermilab as a potential site for C³ and other future facilities.