Compact linear collider
The Compact Linear Collider (CLIC) is a concept of a future linear accelerator that is intended to further increase the limit of attainable center of gravity energies in high-energy physics . In the CLIC, electrons and positrons are to be accelerated and brought to collision. The project is currently the only mature planning variant for such a linear accelerator in the energy range up to several T eV . The accelerator would have a length between 11 and 50 km, which is more than ten times longer than the Stanford Linear Accelerator in Stanford , California . There are plans to build CLIC at CERN near Geneva as a cross-border project between France and Switzerland . Construction is scheduled to start in 2026 and commissioning is scheduled for 2035, when the Large Hadron Collider at CERN could have ceased operations.
CLIC would use a novel two-beam accelerator technique with an acceleration gradient of 100 MV / m. It is planned to expand CLIC in three stages so that particle collisions can take place at three different center of gravity energies of up to 3 TeV in order to be able to explore the possible spectrum of new physics in the entire energy range in the best possible way. At present, further research and development work is necessary in order to be able to carry out high-precision physical measurements under the difficult conditions of such a particle beam and to block out disturbing background effects.
The aim of CLIC is to discover physics beyond the Standard Model , both via precision measurements of predicted physical quantities and via the direct detection of previously unknown particles . Due to its design as an electron-positron collider, the CLIC would be highly sensitive to deviations in the electroweak sector of the standard model, the precision of which would exceed that of the LHC. The current planning of the CLIC also includes the possibility of polarizing the particle beams.
background
There are two main types of particle accelerators, which differ in the way which particles are accelerated: Leptons such as electrons and positrons or hadrons , in particular protons and antiprotons. Hadrons are particles made up of partons that lead to more complex collision events. Every such event must be divided into the "hard" process, in which two of the components of the hadrons interact with each other, and a background process, in which the fragments of the hadrons re- hadronize . Furthermore, it is not known which momentum the interacting partons had, only the momentum of the complete hadron. This limits the maximum achievable precision of the measurements. Leptons, on the other hand, are elementary particles , so the exact initial state in the collision event is known and fewer other particles are generated in the collision.
On the other hand, hadrons have a higher mass than leptons and can therefore be accelerated to higher energies than leptons in a ring accelerator due to the lower energy losses caused by synchrotron radiation . Lepton accelerators are therefore usually designed as linear accelerators with a considerably higher space requirement.
Expansion stages
A three-stage expansion is planned for CLIC, with the first stage operating at 380 GeV, the second at 1.5 TeV and the third at 3 TeV. The integrated luminosity of the individual levels should be 1 from −1 , 2.5 from −1 and 5 from −1 , respectively, over a period of 27 years . The choice of these center of gravity energies is based on the current data obtained by the LHC and an investigation by the CLIC study.
Even at 380 GeV, CLIC would cover the entire physics of the standard model; Energies beyond this limit allow the discovery of new physics as well as precision measurements within the Standard Model. In addition, CLIC will operate in the area around 350 GeV, which represents the threshold for generating top- antitope pairs, with the aim of determining the properties of the top more precisely.
Objects of investigation
Higgs physics
So far, all results of the LHC experiments on the Higgs boson are in line with the expectations of the Standard Model. However, these experiments can only test some predictions with large measurement uncertainties. CLIC could measure some parameters, particularly the strength of the Higgs couplings to other particles, with greater precision. The expansion stage at 380 GeV allowed, for example, precise model-independent measurements of the Higgs-boson couplings to fermions and bosons via Higgs radiation and vector boson fusion processes. The second and third expansion stages would enable access to phenomena such as coupling to the top quark, rare Higgs decays and the Higgs self-interaction.
Top physics
The top quark, the heaviest known elementary particle, has not yet been investigated in electron-positron colliders. A primary goal of the planned top program at CLIC is to investigate the energy threshold for top antitop production at around 350 GeV in order to precisely determine the mass of the top and other properties. For these investigations, 10% of the duration of the first expansion stage with an integrated luminosity of 100 fb −1 in total are planned. With the help of these studies, the top mass could be determined more precisely in a theoretically well-defined way than is possible in hadron colliders. Further goals of CLIC would be to measure the electroweak couplings of the top quark to the Z boson and the photon , as deviations from the predictions of the Standard Model would be an indication of new physics. The observation of top decays with flavor changing neutral currents , the flavor changing neutral currents , at the CLIC would be an indirect indication of new physics, since these must not occur in the standard model at the CLIC.
New phenomena
CLIC could discover new physics either through indirect measurements or direct observations. Significant deviations from the properties of the particles predicted by the Standard Model in precision measurements would be such an indirect signal. These indirect methods give insight into energy scales far above the achievable focus energy up to a few tens of TeV.
Examples of indirect measurements that would be possible with CLIC at 3 TeV: Use of the production of muon- antimyon pairs to obtain indications of a Z'-boson (up to approx. 30 TeV), which indicates an additional calibration group ; Use of vector boson scattering to gain insight into the mechanism of electroweak symmetry breaking ; Using the combination of different final states in the Higgs decay to determine the fundamental or composite nature of the Higgs boson (up to about 50 TeV).
Direct pair production of particles up to a mass of 1.5 TeV and the production of single particles up to a mass of 3 TeV are also possible with CLIC. Due to fewer disturbing background events at lepton colliders, it would be possible at the CLIC to measure these potential new particles with high accuracy. Examples of such particles that CLIC could observe directly would be some predicted by supersymmetry : Charginos , Neutralinos, and Sleptonen .
status
In 2017 approximately 2% of the annual CERN budget was invested in the development of CLIC. The first phase of the CLIC with a length of approximately 11 kilometers will take an estimated 6 billion Swiss francs. CLIC is an international project to which more than 70 institutes in more than 30 countries contribute. It consists of two collaborations: the CLIC detector and physics collaboration (CLICdp) and the CLIC accelerator study . CLIC is currently in the development phase, with performance studies for accelerator parts and systems as well as detector technologies being carried out as well as optimization studies and analysis methods being developed. In parallel, the collaborations work with groups from theoretical physics to explore the physical potential of CLIC.
CLIC has submitted two short documents as a contribution to the next update of the European Strategy for Particle Physics (ESPP), which summarize the physics potential of CLIC and the status of the accelerator and detector projects at CLIC. The update of the ESPP is a process in the entire physics community, which is expected to be completed in May 2020 with the publication of a new strategy paper.
Detailed information about the CLIC project can be found in the CERN Yellow Reports on the potential for new physics, the implementation plan and detector technologies. An overview is given in the 2018 CLIC Summary Report .
Individual evidence
- ↑ a b c d e f g h i j Philip N. Burrows et al .: The Compact Linear Collider (CLIC) - 2018 Summary Report . In: CERN Yellow Reports . CERN-2018-005-M, 2018, ISBN 978-92-9083-507-3 , doi : 10.23731 / CYRM-2018-002 , arxiv : 1812.06018 (English).
- ^ ATLAS collaboration: Observation of a New Particle in the Search for the Standard Model Higgs Boson with the ATLAS Detector at the LHC . In: Physics Letters B . tape 716 , no. 1 , 2012, p. 1–29 , doi : 10.1016 / j.physletb.2012.08.020 , arxiv : 1207.7214 (English).
- ^ The CMS collaboration: Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC . In: Physics Letters B . tape 716 , no. 1 , 2012, p. 30–61 , doi : 10.1016 / j.physletb.2012.08.021 , arxiv : 1207.7235 (English).
- ↑ a b Conceptual Design Report CLIC CDR. In: CLIC detector and physics study. CERN, accessed on August 23, 2019 .
- ↑ a b H. Abramowicz et al .: Higgs Physics at the CLIC Electron-Positron Linear Collider . In: European Physical Journal C . tape 77 , no. 7 , 2017, p. 475 , doi : 10.1140 / epjc / s10052-017-4968-5 , arxiv : 1608.07538 (English).
- ↑ a b H. Abramowicz et al .: Top-Quark Physics at the CLIC Electron-Positron Linear Collider . 2018, arxiv : 1807.02441 (English).
- ↑ a b c J. de Blas et al .: The CLIC Potential for New Physics . In: CERN Yellow Reports . CERN-2018-009-M, 2018, ISBN 978-92-9083-511-0 , doi : 10.23731 / CYRN-2018-003 , arxiv : 1812.02093 (English).
- ^ P. Roloff et al .: The Compact Linear e + e - Collider (CLIC): Physics Potential . 2018, arxiv : 1812.07986 (English).
- ^ A. Robson et al .: The Compact Linear e + e - Collider (CLIC): Accelerator and Detector . 2018, arxiv : 1812.07987 (English).
- ↑ M. Aicheler et al .: The Compact Linear Collider (CLIC) - Project Implementation Plan . In: CERN Yellow Reports . CERN-2018-010-M, 2018, doi : 10.23731 / CYRM-2018-004 (English).
- ^ D. Dannheim et al .: Detector Technologies for CLIC . In: CERN Yellow Reports . CERN-2019-001, 2019, doi : 10.23731 / CYRM-2019-001 , arxiv : 1905.02520 (English).