Editing CERN Axion Solar Telescope (section)

== Results ==
The CAST experiment began with the goal of devising new methods and implementing novel technologies for the detection of solar axions. Owing to the inter-disciplinary and interrelated field of axion studies, [[dark matter]], [[dark energy]], and axion-like exotic particles, the new collaborations at CAST have broadened their research into the wide field of [[astroparticle physics]]. Results from these different domains are described below.

=== Constraints on axions ===
During the initial years, axion detection was the primary goal of CAST. Although the CAST experiment did not yet observe axions directly, it has constraint the search parameters. Mass and the [[coupling constant]] of an axion are primary aspects of its detectability.  Over almost 20 years of the operation period, CAST has added very significant details and limitations to the properties of solar axions and axion-like particles.<ref>{{Cite journal|last1=Irastorza|first1=Igor G.|last2=Redondo|first2=Javier|date=September 2018|title=New experimental approaches in the search for axion-like particles|journal=Progress in Particle and Nuclear Physics|volume=102|pages=89–159|doi=10.1016/j.ppnp.2018.05.003|arxiv=1801.08127|bibcode=2018PrPNP.102...89I|s2cid=119471148}}</ref><ref>{{Cite web|date=2018-08-31|title=Search for WISPs gains momentum|url=https://cerncourier.com/a/search-for-wisps-gains-momentum/|access-date=2021-06-23|website=CERN Courier|language=en-GB}}</ref> In the initial run period, the first three CAST detectors put an upper limit of <math>\mathrm{8.8 \times 10^{-11} GeV^{-1}} </math> on <math>g_{a\gamma}</math> (parameter for axion-photon coupling) with a 95% [[Confidence interval|confidence limit]] (CL) for axion mass-  <math>\mathrm{m_{a}\lesssim 0.02 eV} </math>.<ref>{{Cite journal|last=CAST Collaboration|date=2007-04-17|title=An improved limit on the axion-photon coupling from the CAST experiment|journal=Journal of Cosmology and Astroparticle Physics|volume=2007|issue=4|pages=010|doi=10.1088/1475-7516/2007/04/010|arxiv=hep-ex/0702006|bibcode=2007JCAP...04..010A|s2cid=119067481 |issn=1475-7516}}</ref>  For axion mass range between  <math> \mathrm{34.6771 \mu eV}</math> and <math> \mathrm{34.6738 \mu eV}</math>,  RADES constrained the axion-photon coupling constant <math>\mathrm{g_{a\gamma} \gtrsim 4 \times 10^{-13} GeV^{-1}}</math> with just about 5% error.<ref name=":4" /> The most recent results, in 2017 set an upper limit on  <math>g_{a\gamma}</math> <math>\mathrm{< 0.66 \times 10^{-10} GeV^{-1}}</math> (with 95% CL)  for all axions with masses below 0.02 eV.<ref name=":5" /><ref>{{Cite web|title=CAST: from Solar to Dark Matter Axions searches|url=https://ep-news.web.cern.ch/content/cast-solar-dark-matter-axions-searches|access-date=2021-06-23|website=EP News|language=en}}</ref> CAST has thus improved the previous astrophysical limits and has probed numerous relevant axion models of sub-electron-volt mass.<ref>{{Cite web|title=BabyIAXO submits for publication its Conceptual Design Report|url=https://ep-news.web.cern.ch/content/babyiaxo-submits-publication-its-conceptual-design-report|access-date=2021-06-23|website=EP News|language=en}}</ref>

=== Search for dark matter ===
CAST was able to constrain the axion-photon coupling constant from the very low up to the [[hot dark matter]] sector; and the current search range overlaps with the present cosmic hot dark matter bound which is axion mass, <math>m_a \lesssim 0.9 eV</math>.<ref name=":8">{{Cite web|title=CAST in Time – The Quest for Axions and Chameleons|url=https://ep-news.web.cern.ch/content/cast-time-quest-axions-and-chameleons|access-date=2021-06-23|website=EP News|language=en}}</ref><ref name=":2" /> The new detectors at CAST are also looking for proposed dark matter candidates such as the [[Chameleon particle|solar chameleons]] and pharaphotons as well as the relic axions from the [[Big Bang|Big bang]] and [[Inflation (cosmology)|Inflation]].<ref name=":8" /><ref>{{Cite web|title=CAST opens a new window into dark energy and dark matter after 11 years of operation and continuous renewal.|url=https://ep-news.web.cern.ch/content/cast-opens-new-window-dark-energy-and-dark-matter-after-11-years-operation-and-continuous|access-date=2021-06-23|website=EP News|language=en}}</ref> In late 2017, the CAST helioscope which originally was searching for solar axion and ALPs, was converted into haloscope to hunt for the Dark Matter wind in [[Milky Way|milky way]]'s [[galactic halo]] while it crosses the Earth. These idea of streaming dark wind is thought to affect and cause the random and anisotropic orientation of [[solar flare]]s, for which the CAST haloscope will serve as a testbed.<ref>{{Cite web|title=OSQAR experiment sheds light on a hidden sector of CERN's scientific heritage|url=https://ep-news.web.cern.ch/content/osqar-experiment-sheds-light-hidden-sector-cerns-scientific-heritage|access-date=2021-06-23|website=EP News|language=en}}</ref><ref>{{Cite web|title=Search for axions in streaming dark matter|url=https://ep-news.web.cern.ch/content/search-axions-streaming-dark-matter|access-date=2021-06-23|website=EP News|language=en}}</ref><ref>{{Cite web|date=2017-09-22|title=Study links solar activity to exotic dark matter|url=https://cerncourier.com/a/study-links-solar-activity-to-exotic-dark-matter/|access-date=2021-06-23|website=CERN Courier|language=en-GB}}</ref>

=== Search for dark energy ===
In the [[dark energy]] domain CAST is currently looking for signatures of a chameleon, which is hypothesized to be a particle produced when dark energy interacts with the photons. This area is currently in its beginning stages, wherein possible ways of dark energy particles coupling with normal matter are being theorized.<ref>{{Cite web|date=2019-01-24|title=Colliders join the hunt for dark energy|url=https://cerncourier.com/a/colliders-join-the-hunt-for-dark-energy/|access-date=2021-06-23|website=CERN Courier|language=en-GB}}</ref> Using the GridPix detector, the upper bound on the chameleon photon coupling constant- <math>\beta_{\gamma}</math> was determined to be equal to  <math>5.74 \times 10^{10} </math> for <math>\beta_m</math> (chameleon matter coupling constant) in the range of 1 to <math>10^{6}</math>.<ref name=":6" /> KWISP detector obtained an upper limit on the force acting on its detector membrane due to chameleons as <math>44\pm18 </math> pNewton, which corresponds to a specific exclusion zone in <math>\beta_{\gamma}</math>-<math>\beta_m</math> plane and complements the results obtained by GridPix.<ref name=":7" /><ref>{{Cite web|title=KWISP detector searches for dark energy from the Sun|url=https://home.cern/news/news/physics/kwisp-detector-searches-dark-energy-sun|access-date=2021-06-23|website=CERN|language=en}}</ref>