The Compact Linear Collider (CLIC) is a proposed accelerator that is being designed as an addition to CERN’s accelerator complex. Its objective is to collide electrons and positrons (antielectrons) head-on at energies of up to several teraelectronvolts (TeV). For an optimal exploitation of its physics potential, CLIC is intended to be built and operated in three stages, at collision energies of 380 GeV, 1.5 TeV and 3 TeV respectively, for a site length ranging from 11 to 50 km.

The physics aims of CLIC include high-precision measurements of the Higgs boson’s interactions with other particles and with itself. Unlike protons, electrons and positrons are truly point-like elementary particles. Therefore, compared to proton–proton collisions at the LHC, electron–positron collisions at CLIC could provide complementary and more accurate information about the Higgs boson.

In addition, precise measurements of the top quark at all three energy stages would provide sensitivity to potential new physics scenarios. Some of the proposed studies at CLIC could even allow physicists to probe phenomena that originate at energies much higher than that of the collisions themselves.

CLIC’s design incorporates radiofrequency (RF) cavities and a two-beam acceleration concept to produce accelerating fields as high as 100 MV per metre. The RF power needed to accelerate the main beam is generated locally by decelerating a second high-intensity electron beam – the “drive beam” – in special power-extraction structures. This would allow collisions of up to 3 TeV, while keeping the size and cost of the project within reach.

The design and technology development for CLIC being is pursued by an international collaboration of more than 70 institutes in more than 30 countries. Accelerator optimisation, technical developments and system tests have resulted in significant progress in recent years including a reduced cost and an increased energy efficiency. The detector concept has been refined using improved software tools and significant progress has been made on technology developments for the tracking and calorimetry systems.

The construction of the first CLIC energy stage is proposed to start by 2026. This would allow the first beams to be available by 2035 to start the CLIC physics programme spanning the following 25 to 30 years.

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