Updated baseline for a staged Compact Linear Collider

Abstract: The Compact Linear Collider (CLIC) is a multi-TeV high-luminosity linear e+e- collider under development. For an optimal exploitation of its physics potential, CLIC is foreseen to be built and operated in a staged approach with three centre-of-mass energy stages ranging from a few hundred GeV up to 3 TeV. The first stage will focus on precision Standard Model physics, in particular Higgs and top-quark measurements. Subsequent stages will focus on measurements of rare Higgs processes, as well as searches for new physics processes and precision measurements of new states, e.g. states previously discovered at LHC or at CLIC itself. In the 2012 CLIC Conceptual Design Report, a fully optimised 3 TeV collider was presented, while the proposed lower energy stages were not studied to the same level of detail. This report presents an updated baseline staging scenario for CLIC. The scenario is the result of a comprehensive study addressing the performance, cost and power of the CLIC accelerator complex as a function of centre-of-mass energy and it targets optimal physics output based on the current physics landscape. The optimised staging scenario foresees three main centre-of-mass energy stages at 380 GeV, 1.5 TeV and 3 TeV for a full CLIC programme spanning 22 years. For the first stage, an alternative to the CLIC drive beam scheme is presented in which the main linac power is produced using X-band klystrons.

• The paper presents an updated baseline design for CLIC that enables a staged approach with 380 GeV, 1.5 TeV, and 3 TeV collision energies to optimize physics outcomes.
• It outlines technical advancements including optimized RF accelerating structures and precise beam dynamics simulations that enhance performance reliability.
• The paper details critical numerical benchmarks such as targeted luminosity, power consumption, and cost estimates to ensure feasibility and future scalability.

An Overview of the Updated Baseline for a Staged Compact Linear Collider (CLIC)

The paper entitled "Updated baseline for a staged Compact Linear Collider" by The CLIC and CLICdp collaborations presents a comprehensive update on the design and plans for implementing a multi-TeV electron-positron collider, namely the Compact Linear Collider (CLIC). This report focuses on optimizing the CLIC design for a staged construction, following advances since the 2012 Conceptual Design Report (CDR), which primarily detailed a 3 TeV collision energy setup. This summary elucidates the technical advancements, staging strategy, numerical results, and implications for future high-energy physics experiments.

Overview of Proposed Staging

The crucial element of the proposed CLIC project is its execution in three principal energy stages: 380 GeV, 1.5 TeV, and 3 TeV. The initial stage at 380 GeV targets precision measurements within the Standard Model paradigm, particularly regarding Higgs boson and top-quark properties. The paper advocates 380 GeV as optimal for enhancing Higgs and top-quark physics, which aligns with the defined stipulations of the current physics landscape. The second and third stages are set to elevate energy to 1.5 TeV and 3 TeV, respectively, allowing extensive exploration of physics beyond the Standard Model (BSM) through various energy levels essential for detecting new phenomena.

Key Numerical Results and Claims

The paper posits critical parameters for each proposed stage. At 380 GeV, an anticipated luminosity of $1.5 \times 10^{34} \, \text{cm}^{-2} \text{s}^{-1}$ aligns with planned performance metrics, ensuring significant outputs for Higgs measurements and top-quark threshold scans. Moreover, estimations predict the power consumption of the initial energy stage at approximately 252 MW, with a scaled cost of CHF 6.7 billion. These figures incorporate long-term operation strategies aimed at fiscal and energy efficiency, underpinning the viability of CLIC's construction and subsequent upgrades.

Performance Optimization

The CLIC design encapsulates advancements in radio-frequency (RF) accelerating structures to enhance gradient performance while reducing breakdown risks. The RF structure's gradient efficiency is a central focus, affecting cost and performance. High-gradient prototypes exceeding the 100 MV/m benchmark illustrate improvements yet require continued R&D to assure implementation reliability. Furthermore, targeted simulation tools have spearheaded performance estimations, considering beam dynamics and RF limitation challenges.

Discussion on Alternative Configurations

An alternative possibility for the collider's first stage development employs X-band klystrons for RF power generation instead of the drive-beam approach. While klystrons may pose resource challenges at high energies, their incorporation into the 380 GeV stage has been considered reasonable, which necessitates cost-benefit analysis relative to the complete CLIC upgrade strategy.

Implications and Future Developments

CLIC promises a robust energy frontier exploration with implications for high-precision particle physics. This staged approach not only aligns with current theoretical pursuits, such as investigating the Higgs mechanism, but also positions CLIC as a pivotal instrument for potential BSM discoveries. The paper emphasizes CLIC's capacity to operate compliantly with future international scientific directions and contribute to CERN's post-LHC landscape. The output advocates completing necessary technical milestones before the European Strategy for Particle Physics 2019-2020 assessment, which will influence subsequent actions regarding the collider's practical and scientific evolution.

In conclusion, the CLIC paper details a pragmatic design for a staged electron-positron collider that balances current feasibility with future capabilities, demonstrating a thoughtful adaptation of its technological and economic framework for realizing the next phase in particle physics research. The research team asserts a confident outlook toward the eventual implementation, pending further R&D and operational planning refinements requisite for transitioning from conceptualization to reality.