Compact Linear Collider
CLIC is proposed to be built at CERN, across the border between France and Switzerland near Geneva, with first beams starting by the time the Large Hadron Collider (LHC) has finished operations around 2035.
[1] Research and development (R&D) are being carried out to achieve the high precision physics goals under challenging beam and background conditions.
The collider would offer high sensitivity to electroweak states, exceeding the predicted precision of the full LHC programme.
The CLIC collaboration produced a Conceptual Design Report (CDR) in 2012,[2] complemented by an updated energy staging scenario in 2016.
[3] Additional detailed studies of the physics case for CLIC, an advanced design of the accelerator complex and the detector, as well as numerous R&D results are summarised in a recent series of CERN Yellow Reports.
Hadrons are compound objects, which lead to more complicated collision events and limit the achievable precision of physics measurements.
They will have to be accelerated to much higher speeds than heavier particles (baryons) in order to gain the same energy, and suddenly synchrotron loss becomes the limiting factor.
It still has to tackle the problems of not being able to recirculate its beams, though, which despite it being called "compact", necessitates massive scale and a rather unconventional design to reach the high linear accelerations required.
[1] CLIC would allow the exploration of new energy ranges, provide possible solutions to unanswered problems, and enable the discovery of phenomena beyond our current understanding.
[1] This study would allow the top quark mass to be ascertained in a theoretically well-defined manner and at a higher precision than possible with hadron colliders.
[2] CLIC would also aim to measure the top quark electroweak couplings to the Z boson and the photon, as deviations of these values from those predicted by the Standard Model could be evidence of new physics phenomena, such as extra dimensions.
Large deviations in precision measurements of particle properties from the Standard Model prediction would indirectly signal the presence of new physics.
Examples of indirect measurements CLIC would be capable of at 3 TeV are: using the production of muon pairs to provide evidence of a Z′ boson (reach up to ~30 TeV) indicating a simple gauge extension beyond the Standard Model; using vector boson scattering for giving insight into the mechanism of electroweak symmetry breaking; and exploiting the combination of several final states to determine the elementary or composite nature of the Higgs boson (reach of compositeness scale up to ~50 TeV).
Due to the clean environment of electron-positron colliders, CLIC would be able to measure the properties of these potential new particles to a very high precision.
[4] However, research from experimental data on the cosmological constant, LIGO noise, and pulsar timing, suggests it's very unlikely that there are any new particles with masses much higher than those which can be found in the standard model or the LHC.
[14] The high accelerating gradient and the target BDR value (3 × 10−7 pulse−1m−1) drive most of the beam parameters and machine design.
The final time structure of the beam is made of several (up to 25) 244 ns-long trains of bunches at 12 GHz, spaced by gaps of about 5.5 μs.
[5]The main technology challenges of the CLIC accelerator design have been successfully addressed in various test facilities.
The Drive Beam production and recombination, and the two-beam acceleration concept were demonstrated at the CLIC Test Facility 3 (CTF3).
[16][17] These facilities provide the RF power and infrastructure required for the conditioning and verification of the performance of CLIC accelerating structures, and other X-band based projects.
CLICdet consists of four main layers of increasing radius: vertex and tracking system, calorimeters, solenoid magnet, and muon detector.
[19] The vertex and tracking system is located at the innermost region of CLICdet and aims to detect the position and momenta of particles with minimum adverse impact on their energy and trajectory.
[19] The detector also has a luminosity calorimeter (LumiCal) to measure the products of Bhabha scattering events, a beam calorimeter to complete the ECAL coverage down to 10 mrads polar angle, and an intra-train feedback system to counteract luminosity loss due to relative beam-beam offsets.
[21][22] To allow for effective air cooling, the average power consumption of the Silicon sensors in the vertex detector needs to be lowered.
