Editing Compact Linear Collider (section)

== Physics case for CLIC ==
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.

=== Higgs physics ===
The current LHC data suggest that the particle found in 2012 is the [[Higgs boson]] as predicted by the [[Standard Model]] of particle physics.<ref name=atlas>
{{Cite journal
 |author=ATLAS collaboration
 |year=2012
 |title=Observation of a New Particle in the Search for the Standard Model Higgs Boson with the ATLAS Detector at the LHC
 |journal=[[Physics Letters B]]
 |volume=716 |issue=1 |pages=1–29
 |arxiv=1207.7214
 |doi=10.1016/j.physletb.2012.08.020 |doi-access=free
 |bibcode=2012PhLB..716....1A|author-link=ATLAS experiment
}}</ref><ref>{{Cite journal|last=The CMS Collaboration|date=September 2012|title=Observation of a new boson at a mass of 125&nbsp;GeV with the CMS experiment at the LHC|journal=Physics Letters B|volume=716|issue=1|pages=30–61|doi=10.1016/j.physletb.2012.08.021|arxiv=1207.7235|bibcode=2012PhLB..716...30C}}</ref> However, the LHC can only partially answer questions about the true nature of this particle, such as its composite/fundamental nature, [[coupling constant|coupling strengths]], and possible role in an extended electroweak sector.<ref name=cdr_page /> CLIC could examine these questions in more depth by measuring the Higgs couplings to a precision not achieved before.<ref name=Abramovicz_CLIC_CERN-2012>
{{Cite journal
 |last=Abramowicz |first=H.
 |display-authors=etal 
 |year=2017
 |title=Higgs Physics at the CLIC Electron-Positron Linear Collider
 |journal=[[European Physical Journal C]]
 |volume=77 |issue=7 |pages=475
 |arxiv=1608.07538
 |doi=10.1140/epjc/s10052-017-4968-5 |doi-access=free
 |pmid=28943795
 |pmc=5587080
 |bibcode=2017EPJC...77..475A
}}</ref> The 380&nbsp;GeV stage of CLIC allows, for example, accurate model-independent measurements of Higgs [[boson]] couplings to [[fermions]] and bosons through the Higgsstrahlung and WW-fusion production processes. The second and third stages give access to phenomena such as the [[Yukawa interaction|top-Yukawa coupling]], rare Higgs decays and the Higgs self-coupling.<ref name=Abramovicz_CLIC_CERN-2012/>

=== Top-quark physics ===
[[File:Ttbar 3TeV event11 woverlay Tight zoom.png|alt=|thumb|280x280px|A top quark event at 3&nbsp;TeV reconstructed in a simulated detector for CLIC]]
The top quark, the heaviest of all known fundamental particles, has currently never been studied in [[electron]]-[[positron]] collisions.<ref name=top_quark>
{{cite journal |arxiv=1807.02441|collaboration=The CLICdp collaboration|title=Top-quark physics at the CLIC electron-positron linear collider|year=2019|last1=Abramowicz |first1=H. |last2=Alipour Tehrani |first2=N. |last3=Arominski |first3=D. |last4=Benhammou |first4=Y. |last5=Benoit |first5=M. |last6=Blaising |first6=J.-J. |last7=Boronat |first7=M. |last8=Borysov |first8=O. |last9=Bosley |first9=R. R. |last10=Božović Jelisavčić |first10=I. |last11=Boyko |first11=I. |last12=Brass |first12=S. |last13=Brondolin |first13=E. |last14=Bruckman De Renstrom |first14=P. |last15=Buckland |first15=M. |last16=Burrows |first16=P. N. |last17=Chefdeville |first17=M. |last18=Chekanov |first18=S. |last19=Coates |first19=T. |last20=Dannheim |first20=D. |last21=Demarteau |first21=M. |last22=Denizli |first22=H. |last23=Durieux |first23=G. |last24=Eigen |first24=G. |last25=Elsener |first25=K. |last26=Fullana |first26=E. |last27=Fuster |first27=J. |last28=Gabriel |first28=M. |last29=Gaede |first29=F. |last30=García |first30=I.|journal=Journal of High Energy Physics|volume=2019|issue=11|page=003|display-authors=1|doi=10.1007/JHEP11(2019)003|bibcode=2019JHEP...11..003C|s2cid=85505969
}}</ref> The CLIC linear collider plans to have an extensive top quark physics programme. A major aim of this programme would be a threshold scan around the top quark pair-production threshold (~350&nbsp;GeV) to precisely determine the [[mass]] and other significant properties of the top quark. For this scan, CLIC currently plans to devote 10% of the running time of the first stage, collecting 100&nbsp;fb<sup>−1</sup>.<ref name=Burrows_CLIC_CERN-2018/> 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.<ref name=cdr_page/> CLIC would also aim to measure the top quark electroweak couplings to the [[W and Z bosons|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. Further observation of top quark decays with [[Flavour (particle physics)|flavour]]-changing neutral currents at CLIC would be an indirect indication of new physics, as these should not be seen by CLIC under current [[Standard Model]] predictions.<ref name=top_quark/>

=== New phenomena ===
CLIC could discover new physics phenomena either through indirect measurements or by direct observation. Large deviations in precision measurements of particle properties from the [[Standard Model]] prediction would indirectly signal the presence of new physics. Such indirect methods give access to energy scales far beyond the available collision energy, reaching sensitivities of up to tens of TeV.

Examples of indirect measurements CLIC would be capable of at 3&nbsp;TeV are: using the production of muon pairs to provide evidence of a Z{{prime}} boson (reach up to ~30&nbsp;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&nbsp;TeV).<ref name="new_physics_rep">
{{cite journal |last1=de Blas |first1=J. |last2=Franceschini |first2=R. |last3=Riva |first3=F. |last4=Roloff |first4=P. |last5=Schnoor |first5=U. |last6=Spannowsky |first6=M. |last7=Wells |first7=J. D. |last8=Wulzer |first8=A. |last9=Zupan |first9=J. |title=The CLIC potential for new physics |date=21 December 2018 |journal=CERN Yellow Reports: Monographs |volume=3 |doi=10.23731/CYRM-2018-003 |bibcode=2018arXiv181202093D |arxiv=1812.02093 |s2cid=117485395
}}</ref> Direct pair production of particles up to a mass of 1.5&nbsp;TeV, and single particle production up to a mass of 3&nbsp;TeV is possible at CLIC. 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.<ref name="Burrows_CLIC_CERN-2018" /> Examples of particles CLIC could directly observe at 3&nbsp;TeV are some of those proposed by the [[supersymmetry|supersymmetry theory]]: [[chargino]]s, [[neutralino]]s (both ~≤ 1.5&nbsp;TeV), and [[sfermions#Sleptons|sleptons]] (≤ 1.5&nbsp;TeV).<ref name=new_physics_rep/>

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.<ref name="cosmological-bounds">
{{cite journal |last1=Afshordi |first1=Niayesh |last2=Nelson |first2=Elliot |title=Cosmological bounds on TeV-scale physics and beyond |url=https://journals.aps.org/prd/abstract/10.1103/PhysRevD.93.083505 |journal=Physical Review D |access-date=20 February 2023 |pages=083505 |doi=10.1103/PhysRevD.93.083505 |date=7 April 2016|volume=93 |issue=8 |arxiv=1504.00012 |bibcode=2016PhRvD..93h3505A |s2cid=119110506
}}</ref><ref name="ligo-noise">
{{cite arXiv |last1=Afshordi |first1=Niayesh |title=On the origin of the LIGO "mystery" noise and the high energy particle physics desert |date=21 November 2019|class=gr-qc |eprint=1911.09384
}}</ref><ref name="pulsar-timing">
{{cite arXiv |last1=Afshordi |first1=Niayesh |last2=Kim |first2=Hyungjin |last3=Nelson |first3=Elliot |title=Pulsar Timing Constraints on Physics Beyond the Standard Model |date=15 March 2017|class=hep-th |eprint=1703.05331
}}</ref> On the other hand, this research has also indicated that [[quantum gravity]] or [[perturbative]] [[quantum field theory]] will become strongly coupled before 1 PeV, leading to other new physics in the TeVs.<ref name="cosmological-bounds" />