The annual workshop of the Compact Linear Collider (CLIC), a proposed multi-TeV linear electron–positron collider at CERN, attracted more than 200 participants to CERN between 21 and 25 January. CLIC occupies a unique position in both the precision and energy frontiers, combining the benefits of electron–positron collisions with the possibility of multi-TeV collision energies. It uses a two-beam acceleration scheme based on novel, high-gradient X-band accelerating structures, and envisions a three-stage implementation with a collision energy stepping from 380 GeV to 3 TeV and a diverse physics programme spanning 30 years (CERN Courier November 2016, p21).
Key CLIC concepts such as drive-beam production and operation of high-efficiency radio-frequency cavities have all been demonstrated, reported Steinar Stapnes, CLIC project leader: “The CLIC project offers a cost-effective and innovative technology and is ready to proceed towards construction with a Technical Design Report, enabling the start of construction for the first stage by 2026 and realising electron–positron collisions at 380 GeV as soon as 2035,” he said.
A major focus during 2018 was the completion of a project implementation plan, as well as several comprehensive CERN Yellow Reports describing the CLIC accelerator, detector, and detailed physics studies. A central point was un updated cost and power estimate, which for the 380 GeV stage amount to around 5.9 billion CHF and 168 MW. Workshop participants also discussed the next important step for CLIC: a preparatory phase focusing on large-scale tests, industrial production and civil-engineering aspects including siting and infrastructure.
An overview of potential industrial involvement in the CLIC core technologies is also being compiled. Several partner agreements support technical developments for smaller X-band based accelerators, including the European Commission’s CompactLight study and the recently proposed eSPS project that would see a 3.5 GeV X-band electron linac feeding the Super Proton Synchrotron for further acceleration, followed by slow extraction to study dark-sector physics. The linear tunnel of CLIC also provides a natural infrastructure for long-term future projects based on plasma-wakefield and other acceleration techniques.
Concerning CLIC detector R&D, the latest test-beam analysis and simulation results show promise for the challenging vertex and tracker requirements at CLIC. The next generation of detector assemblies will be tested at DESY in Hamburg, where the CLICdp vertex and tracker group will be welcomed for several weeks during the current long shutdown of CERN’s accelerators.
CLIC’s physics programme generated rich discussions at the January workshop. In particular the Higgs self-coupling, which determines the shape of the Higgs potential, can be directly accessed at the multi-TeV collisions at CLIC via double-Higgs production. A series of joint talks between theorists and experimentalists, as part of a dedicated mini-workshop, also covered CLIC’s potential to extend our knowledge of physics beyond the Standard Model, including possible compositeness of the Higgs boson and dark-matter candidates such as the thermal Higgsino and axion-like particles. The full physics case, designs, costs and timescales for CLIC were submitted to the European Strategy for Particle Physics Update in December.
Read the full report on the CLIC website.