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The International Linear Collider: A Global Project

Philip Bambade, Tim Barklow, Ties Behnke, Mikael Berggren, James Brau, Philip Burrows, Dmitri Denisov, Angeles Faus-Golfe, Brian Foster, Keisuke Fujii, Juan Fuster, Frank Gaede, Paul Grannis, Christophe Grojean, Andrew Hutton, Benno List, Jenny List, Shinichiro Michizono, Akiya Miyamoto, Olivier Napoly, Michael Peskin, Roman Poeschl, Frank Simon, Jan Strube, Junping Tian, Maksym Titov, Marcel Vos, Andrew White, Graham Wilson, Akira Yamamoto, Hitoshi Yamamoto, Kaoru Yokoya

TL;DR

The International Linear Collider (ILC) is proposed as a mature, energy-upgradable $e^+e^-$ facility designed to deliver precision Higgs, top-quark, and electroweak measurements with polarized beams. By operating at $250$ GeV initially and upgrading to higher energies, the ILC enables model-independent Higgs coupling extractions via EFT, direct measurements of Higgs self-coupling and top Yukawa coupling, and robust direct searches for weakly-coupled new states. Its detector concepts (ILD and SiD) and a globally industrialized SCRF-based accelerator underpin full-simulation-based projections that outperform HL-LHC in certain precision domains and complement it in others. The project emphasizes flexibility, risk mitigation, and international collaboration, with a realistic cost and schedule aligned to build a long-lived facility advancing beyond the current SM paradigm. Altogether, the ILC promises a definitive, multi-decade program to illuminate Higgs physics, electroweak interactions, and potential new physics within reach of next-generation colliders.

Abstract

The International Linear Collider (ILC) is now under consideration as the next global project in particle physics. In this report, we review of all aspects of the ILC program: the physics motivation, the accelerator design, the run plan, the proposed detectors, the experimental measurements on the Higgs boson, the top quark, the couplings of the W and Z bosons, and searches for new particles. We review the important role that polarized beams play in the ILC program. The first stage of the ILC is planned to be a Higgs factory at 250 GeV in the centre of mass. Energy upgrades can naturally be implemented based on the concept of a linear collider. We discuss in detail the ILC program of Higgs boson measurements and the expected precision in the determination of Higgs couplings. We compare the ILC capabilities to those of the HL-LHC and to those of other proposed e+e- Higgs factories. We emphasize throughout that the readiness of the accelerator and the estimates of ILC performance are based on detailed simulations backed by extensive RandD and, for the accelerator technology, operational experience.

The International Linear Collider: A Global Project

TL;DR

The International Linear Collider (ILC) is proposed as a mature, energy-upgradable facility designed to deliver precision Higgs, top-quark, and electroweak measurements with polarized beams. By operating at GeV initially and upgrading to higher energies, the ILC enables model-independent Higgs coupling extractions via EFT, direct measurements of Higgs self-coupling and top Yukawa coupling, and robust direct searches for weakly-coupled new states. Its detector concepts (ILD and SiD) and a globally industrialized SCRF-based accelerator underpin full-simulation-based projections that outperform HL-LHC in certain precision domains and complement it in others. The project emphasizes flexibility, risk mitigation, and international collaboration, with a realistic cost and schedule aligned to build a long-lived facility advancing beyond the current SM paradigm. Altogether, the ILC promises a definitive, multi-decade program to illuminate Higgs physics, electroweak interactions, and potential new physics within reach of next-generation colliders.

Abstract

The International Linear Collider (ILC) is now under consideration as the next global project in particle physics. In this report, we review of all aspects of the ILC program: the physics motivation, the accelerator design, the run plan, the proposed detectors, the experimental measurements on the Higgs boson, the top quark, the couplings of the W and Z bosons, and searches for new particles. We review the important role that polarized beams play in the ILC program. The first stage of the ILC is planned to be a Higgs factory at 250 GeV in the centre of mass. Energy upgrades can naturally be implemented based on the concept of a linear collider. We discuss in detail the ILC program of Higgs boson measurements and the expected precision in the determination of Higgs couplings. We compare the ILC capabilities to those of the HL-LHC and to those of other proposed e+e- Higgs factories. We emphasize throughout that the readiness of the accelerator and the estimates of ILC performance are based on detailed simulations backed by extensive RandD and, for the accelerator technology, operational experience.

Paper Structure

This paper contains 142 sections, 27 equations, 88 figures, 20 tables.

Table of Contents

  1. Introduction
  2. ILC Machine Design
  3. Design evolution since the TDR
  4. Superconducting RF Technology
  5. The quest for high gradients
  6. Gradient impact on costs:
  7. Gradient limitations:
  8. Results from E-XFEL cavity production:
  9. High-gradient R&D -- nitrogen infusion:
  10. High-gradient R&D -- alternative cavity shapes:
  11. Further cost reduction R&D
  12. Low $RRR$ material:
  13. Ingot and large-grain niobium:
  14. Basic parameters
  15. Cavities
  16. ...and 127 more sections

Figures (88)

  • Figure 1: Schematic layout of the ILC in the $250\,{\mathrm{GeV}}$ staged configuration.
  • Figure 2: A $1.3\,{\mathrm{GHz}}$ superconducting niobium nine-cell cavity.
  • Figure 3: An ILC type cryomodule. © Rey.Hori/KEK.
  • Figure 4: Development of the gradient of SRF cavities since 1970 Geng:2015glc.
  • Figure 5: Examples of the $Q_0\,(E_{\mathrm{acc}})$ curves of some of the best cavities, either treated at RI using "EP final", or at EZ using "BCP flash." Singer:2016fbf. Vendor "RI" employs a production process that closely follows the ILC specifications, with a final electropolishing step. The ILC gradient / $Q_0$ goals are overlaid.
  • ...and 83 more figures