The International Linear Collider. A Global Project (1901.09829v1)

Abstract: A large, world-wide community of physicists is working to realise an exceptional physics program of energy-frontier, electron-positron collisions with the International Linear Collider (ILC). This program will begin with a central focus on high-precision and model-independent measurements of the Higgs boson couplings. This method of searching for new physics beyond the Standard Model is orthogonal to and complements the LHC physics program. The ILC at 250 GeV will also search for direct new physics in exotic Higgs decays and in pair-production of weakly interacting particles. Polarised electron and positron beams add unique opportunities to the physics reach. The ILC can be upgraded to higher energy, enabling precision studies of the top quark and measurement of the top Yukawa coupling and the Higgs self-coupling. The key accelerator technology, superconducting radio-frequency cavities, has matured. Optimised collider and detector designs, and associated physics analyses, were presented in the ILC Technical Design Report, signed by 2400 scientists. There is a strong interest in Japan to host this international effort. A detailed review of the many aspects of the project is nearing a conclusion in Japan. Now the Japanese government is preparing for a decision on the next phase of international negotiations, that could lead to a project start within a few years. The potential timeline of the ILC project includes an initial phase of about 4 years to obtain international agreements, complete engineering design and prepare construction, and form the requisite international collaboration, followed by a construction phase of 9 years.

• The paper presents a strategic framework for the ILC, emphasizing high-precision Higgs measurements and advances in electron-positron collision techniques.
• The paper details SCRF technology validated through XFEL experiments and outlines phased timelines for international collaboration.
• The paper highlights the ILC's potential to probe beyond-Standard Model physics and to complement LHC discoveries with cleaner experimental data.

The International Linear Collider: A Strategic Framework for Future High Energy Physics

The document encapsulates a comprehensive proposal for the International Linear Collider (ILC), an advanced particle accelerator designed to probe the forefront of particle physics. Within its scope, the ILC aims to complement the Large Hadron Collider (LHC) by providing high-precision and model-independent measurements, notably of the Higgs boson couplings, at the energy frontier of electron-positron collisions. This document outlines the scientific goals, technical specifications, and collaborative undertakings envisioned for the ILC, establishing it as a global project steered by an international consortium of physicists.

The ILC is posited to play an essential role in addressing limitations of the Standard Model (SM), motivating inquiries into new physics through precise experimentation. Specifically, it targets the gaps in the SM related to dark matter, dark energy, and the matter-antimatter asymmetry. The project's strategic objective is high-precision Higgs physics, distinguishing it from the LHC by exploiting electron-positron collisions for cleaner signal environments and enabling unprecedented scrutiny of the Higgs boson's properties, such as its Yukawa and self-couplings.

Technical Design and Project Scope

The core technology of the ILC relies on superconducting radio-frequency (SCRF) cavities, augmented by polarised electron-positron beams to maximise experimental reach. Current SCRF technology levels, validated through free-electron laser experiments such as the European XFEL, render the accelerator ready for deployment. The collider plan envisions a center-of-mass energy initiation at 250 GeV, with potential upgrades enabling exploration at energies up to 1 TeV. These upgrades present opportunities for detailed studies of top quark physics and direct searches for beyond-standard-model phenomena.

The document elaborates on the project's implementation strategy, including a phased timeline that anticipates a 4-year preparatory period covering international agreements and final design, followed by a 9-year construction phase. Japan is highlighted as a potential host country, with ongoing government evaluations and preparatory negotiations indicating robust international support.

Implications and Outlook

The ILC promises a significant theoretical and practical impact on high-energy physics. Its detailed probe into the Higgs sector may reveal deviations indicative of novel physics, which are unobtainable via hadron collider experiments. Moreover, the project enriches the experimental toolkit necessary for precision electroweak measurements and for exploring phenomena like exotic Higgs decays, which are intrinsic to understanding the universe's fundamental processes.

While acknowledging the promising landscape, the paper provides prudent stakeholder insights related to socio-economic aspects, international collaboration frameworks, and the requisite infrastructural commitments. As scientific interest converges across continents, the ILC is also seen as a catalyst for fostering global scientific exchange and for training new generations of physicists.

In conclusion, the document presents a comprehensive evaluation of the ILC as a pivotal endeavor in particle physics. By offering a detailed roadmap for the realization of this large-scale international project, it aims to expand the boundaries of our experimental capabilities and theoretical understanding, setting the stage for future explorations into the underlying principles of matter. The ILC stands as a testament to the collaborative ethos and forward-thinking that define the contemporary physics community, aspiring not only to solve outstanding questions but also to innovate through its pursuit of knowledge.