The Compact Linear Collider (CLIC) - 2018 Summary Report

Abstract: The Compact Linear Collider (CLIC) is a TeV-scale high-luminosity linear $e^+e^-$ collider under development at CERN. Following the CLIC conceptual design published in 2012, this report provides an overview of the CLIC project, its current status, and future developments. It presents the CLIC physics potential and reports on design, technology, and implementation aspects of the accelerator and the detector. CLIC is foreseen to be built and operated in stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, respectively. CLIC uses a two-beam acceleration scheme, in which 12 GHz accelerating structures are powered via a high-current drive beam. For the first stage, an alternative with X-band klystron powering is also considered. CLIC accelerator optimisation, technical developments and system tests have resulted in an increased energy efficiency (power around 170 MW) for the 380 GeV stage, together with a reduced cost estimate at the level of 6 billion CHF. The detector concept has been refined using improved software tools. Significant progress has been made on detector technology developments for the tracking and calorimetry systems. A wide range of CLIC physics studies has been conducted, both through full detector simulations and parametric studies, together providing a broad overview of the CLIC physics potential. Each of the three energy stages adds cornerstones of the full CLIC physics programme, such as Higgs width and couplings, top-quark properties, Higgs self-coupling, direct searches, and many precision electroweak measurements. The interpretation of the combined results gives crucial and accurate insight into new physics, largely complementary to LHC and HL-LHC. The construction of the first CLIC energy stage could start by 2026. First beams would be available by 2035, marking the beginning of a broad CLIC physics programme spanning 25-30 years.

• The paper introduces a novel two-beam acceleration method and refined beam dynamics analysis to achieve multi-TeV collision energies.
• It details a staged energy plan with specific design optimizations, targeting high luminosity and cost-efficient performance.
• The report outlines advanced detector concepts and international collaboration strategies to explore physics beyond the Standard Model.

Overview of the Compact Linear $\Pep\Pem$ Collider (CLIC) 2018 Summary Report

The 2018 Summary Report on the Compact Linear Collider (CLIC) provides an in-depth examination of the design, technology, and potential physics outcomes of the proposed multi-TeV electron-positron collider. Coordinated by the CLIC and CLICdp collaborations, this document outlines the project's current status and envisioned future developments, placing significant emphasis on the feasibility and scientific potential of CLIC.

Accelerator Design and Technology

CLIC represents an ambitious project with a three-stage energy plan: starting at 380 GeV, then advancing to 1.5 TeV, and finally reaching 3 TeV. The collider uses a unique two-beam acceleration scheme with high-gradient, normal-conducting 12 GHz structures, powered by a high-current drive beam. This approach provides a high luminosity, essential for precision measurements and the discovery of new physics.

Key developments in CLIC's accelerator design include improvements in energy efficiency with a targeted 170 MW power consumption for the 380 GeV stage, offering a substantial cost reduction to approximately 6 billion CHF for this initial phase. The alternative scenario of using X-band klystrons for the first stage is also explored, providing flexibility and potential cost benefits depending on further technological advancements.

Beam Dynamics and Luminosity Metrics

The intricacies of CLIC's beam dynamics have been extensively researched, including beam alignment, luminosity optimization, and stability assurance. Techniques such as beam-based alignment and advanced feedback systems are crucial for maintaining the desired beam sizes, which are essential for achieving the high luminosities envisioned across its operational spectrum.

Studies indicate that the proposed solutions, including sub-nanometer quadrupole stabilization, ensure that CLIC's performance goals are not only realistic but also robust in the face of various dynamic imperfections.

Detector Concepts and Physics Performance

The updated CLICdet concept has been optimized for particle flow analysis, consisting of light-weight silicon pixel detectors for tracking, and highly granular calorimeters for precise energy measurements. This design approach supports the delivery of the outstanding spatial resolution and energy resolution needed to extract the maximum potential from CLIC's physics program.

The report emphasizes numerous detector technology R&D developments, from silicon vertex and tracker systems to calorimetry, all aimed at achieving the high precision required for CLIC's ambitious physics objectives.

Physics Potential of CLIC

CLIC's physics reach is extensive, promising significant contributions to Higgs physics, top-quark studies, and searches for Beyond Standard Model (BSM) phenomena. The three-stage energy plan allows for a sequential refinement in precision and discovery potential. The document details exploratory studies that demonstrate CLIC's capability for precise measurements of Higgs boson properties, top-quark characteristics, and electroweak parameters, thereby providing unparalleled insight into extensions of the Standard Model.

Strategic Planning and Future Directions

CLIC is designed with adaptability and extensibility in mind, providing a foundation that could accommodate future developments in novel accelerator technologies, potentially pushing collision energies beyond the initial 3 TeV target. The report underscores a vision for shaping a comprehensive preparation strategy, including modular industrial production, system verification, and collaborative international effort.

The timeline anticipates a construction start around 2026, aiming for first collisions by 2035. This timeline and the accompanying strategic framework ensure that CLIC remains a competitive prospect for advancing high-energy physics research post-LHC.

Conclusion

The 2018 Summary Report effectively captures the transformative potential of CLIC in advancing our understanding of fundamental physics through its meticulously crafted design and technology foundations. By aligning collaborative international efforts and embracing novel technological prospects, CLIC is poised to become a pivotal tool in the exploration of high-energy physics phenomena.