The Compact Linear Collider (CLIC) workshop is the main annual gathering of the CLIC accelerator and detector communities, and this year attracted more than 220 participants to CERN on 22–26 January. CLIC is a proposed electron-positron linear collider envisaged for the era beyond the high-luminosity LHC (HL-LHC), that would operate a staged programme over a period of 25 years with collision energies at 0.38, 1.5, and 3 TeV. This year the CLIC workshop focused on preparations for the update of the European Strategy for Particle Physics in 2019–2020.
The initial CLIC energy stage is optimised to provide high-precision Higgs boson and top-quark measurements, with the higher-energy stages enhancing sensitivity to effects from beyond-Standard Model (BSM) physics (CERN Courier November 2016 p20). Following a 2017 publication on Higgs physics, the workshop heard reports on recent developments in top-quark physics and the BSM potential at CLIC, both of which are attracting significant interest from the theory community.
Speakers also reported extensive progress in the validation and performance of the new detector model. To ensure that its performance meets the challenging specifications, a new approach to tracking has been commissioned, and the particle flow analysis and flavour-tagging capabilities have been consolidated. Updates were presented on the broad and active R&D programme on the vertex and tracking detectors, which aims to find technologies that simultaneously fulfil all the CLIC requirements. Reports were given on test-beam campaigns with both hybrid and monolithic assemblies, and on ideas for future developments. Many of the tracking and calorimeter technologies under study for the CLIC detector are also of interest to the HL-LHC, where the high granularity and time-resolution needed for CLIC are equally crucial.
For the accelerator, studies with the aim of reducing the cost and power have particular priority, presenting the initial CLIC stage as a project requiring resources comparable to what was needed for LHC. Key activities in this context are high-efficiency RF systems, permanent magnet studies, optimised accelerator structures and overall implementation studies related to civil engineering, infrastructure, schedules and tunnel layout.
A key aspect of the ongoing accelerator development is moving towards industrialisation of the component manufacture, by fostering wider applications of the CLIC 12 GHz X-band technology with external partners. In this respect, the CLIC workshop coincided with the kick-off meeting for the CompactLight project recently funded by the Horizon 2020 programme, which aims to design an optimised X-ray free-electron laser based on X-band technology for more compact and efficient accelerators (CERN Courier December 2017 p8).
Last year also saw the realisation of the CERN Linear Electron Accelerator for Research (CLEAR), a new user facility for accelerator R&D whose programme includes CLIC high-gradient and instrumentation studies (CERN Courier November 2017 p8). Presentations at the workshop addressed the programmes for instrumentation and radiation studies, plasma-lensing, wakefield monitors and high-energy electrons for cancer therapy.
During 2018 the CLIC accelerator and detector and physics collaborations will prepare summary reports focusing on the 380 GeV initial CLIC project implementation as inputs for the update of the European Strategy for Particle Physics, including plans for the project preparation phase in 2020–2025.