CERN Axion Solar Telescope

Last updated
CERN Axion Solar Telescope
Successor International Axion Observatory
FormationApproved on 13 April 2000
Legal statusTaking data since 18 June 2003
PurposeSearch for dark matter and energy
Headquarters Geneva, Switzerland
FieldsAstroparticle physics
Spokesperson
Konstantin Zioutas
Website cast.web.cern.ch/CAST/
CAST. The telescope magnet (blue) pivots about the right-hand side, while the yellow gantry on the left of the picture rolls along a circular track in the floor and raises and lowers the left-hand side to track the sun. CAST-Experiment.jpg
CAST. The telescope magnet (blue) pivots about the right-hand side, while the yellow gantry on the left of the picture rolls along a circular track in the floor and raises and lowers the left-hand side to track the sun.

The CERN Axion Solar Telescope (CAST) is an experiment in astroparticle physics to search for axions originating from the Sun. The experiment, sited at CERN in Switzerland, was commissioned in 1999 and came online in 2002 with the first data-taking run starting in May 2003. The successful detection of solar axions would constitute a major discovery in particle physics, and would also open up a brand new window on the astrophysics of the solar core.

Contents

CAST is currently the most sensitive axion helioscope. [1]

Theory and operation

If the axions exist, they may be produced in the Sun's core when X-rays scatter off electrons and protons in the presence of strong electric fields. The experimental setup is built around a 9.26 m long decommissioned test magnet for the LHC capable of producing a field of up to 9.5  T . This strong magnetic field is expected to convert solar axions back into X-rays for subsequent detection by X-ray detectors. The telescope observes the Sun for about 1.5 hours at sunrise and another 1.5 hours at sunset each day. The remaining 21 hours, with the instrument pointing away from the Sun, are spent measuring background axion levels.

Members of the CAST Collaboration, 2011 Castexp1.jpg
Members of the CAST Collaboration, 2011

CAST began operation in 2003 searching for axions up to 0.02  eV . In 2005, Helium-4 was added to the magnet, extending sensitivity to masses up to 0.39 eV, then Helium-3 was used during 2008–2011 for masses up to 1.15 eV. CAST then ran with vacuum again searching for axions below 0.02 eV.

As of 2014, CAST has not turned up definitive evidence for solar axions. It has considerably narrowed down the range of parameters where these elusive particles may exist. CAST has set significant limits on axion coupling to electrons [2] and photons. [3]

A 2017 paper using data from the 2013–2015 run reported a new best limit on axion-photon coupling of 0.66×10−10 / GeV. [4] [5]

Built upon the experience of CAST, a much larger, new-generation, axion helioscope, the International Axion Observatory (IAXO), has been proposed and is now under preparation. [6]

Detectors

The CAST focuses on the solar axions using a helioscope, which is a 9.2 m superconducting LHC prototype dipole magnet. The superconductive magnet is maintained by constantly keeping it at 1.8 Kelvin using superfluid helium. There are two magnetic bores of 43 mm diameter and 9.2 6m length with X-ray detectors placed at all ends. These detectors are sensitive to photons from inverse Primakoff conversion of solar axions. The two X-ray telescopes of CAST measures both signal and background simultaneously with the same detector and reduces the systematic uncertainties. [7] [8]

From 2003 to 2013, the following three detectors were attached to ends of the dipole magnet, all based on the inverse Primakoff effect, to detect the photons converted from the solar axions. [9]

  1. Conventional time projection chamber detectors (TPC).
  2. MICROMEsh GAseous Structure detectors (MICROMEGAS).
  3. X-ray telescope with a charged couple device (CCD).

After 2013 several new detectors such as the RADES, GridPix, and KWISP were installed, with modified goals and newly enhanced technologies. [10]

Conventional time projection chamber detectors (TPC)

TPC is a gas-filled drift chambers type of detector, designed to detect the low-intensity X-ray signals at CAST. The interactions in this detector take place in a very large gaseous chamber and produce ionizing electrons. These electrons travel towards the multiwire proportional chamber (MWPC), where the signal is then amplified through the avalanche process. [11]

MICROMEsh GAseous Structure detectors (MICROMEGAS)

This detector operated during the period of 2002 to 2004. It is a gaseous detector and was primarily employed for to detect X-rays in the energy range of 1–10 KeV. The detector itself was made up of low radioactive materials. The choice of material was mainly based on reducing the background noise, and Micromegas achieved a significantly low background rejection of 6×10−7 counts·keV−1·cm−2·s−1 without any shielding. [10] [12]

X-ray telescope with a charged couple device (CCD)

This detector has a pn-CCD chip located at the focal plane of the X-ray telescope. The X-ray telescope is based on the popular Wolter-I mirror optics concept. This technique is widely used in almost all X-ray astronomy telescopes. Its mirror is made up of 27 gold-coated nickel shells. These parabolic and hyperbolic shells are confocally arranged to optimize the resolution. The largest shell is 163 mm in diameter, while the smallest is 76 mm. The overall mirror system has a focal length of 1.6 m. [9] [13] This detector achieved a remarkably good signal to noise ratio by focusing the axions created inside the magnetic field chamber onto small, about few area. [12]

GridPix detector

In 2016, The GridPix detector was installed to detect the soft X-rays (energy range of 200 eV to 10 KeV) generated by solar chameleons through the primakoff effect. During the search period of 2014 to 2015 the detected signal-to-noise ratio was below the required levels. [14]

InGrid Based X-ray detector

The sole aim of this detector is to enhance the sensitivity of CAST to energy thresholds around 1 KeV range. This is an improved sensitive detector set up in 2014 behind the X-ray telescope, for the search of solar chameleons which have low threshold energies. The InGrid detector and its granular Timepix pad readout with low energy threshold of 0.1 KeV for photon detection hunts the solar chameleons in this range. [8] [15]

A CAST experiment member working at the RADES detector Cast3.jpg
A CAST experiment member working at the RADES detector

Relic Axion Dark Matter Exploratory Setup (RADES)

The RADES started searching for axion-like dark matter in 2018, and the first results from this detector were published in early 2021. Although no significant axion signal was detected above the noise background during the 2018 to 2021 period, RADES became the first detector to search for axions above . CAST helioscope (looks at sun) was made a haloscope (looks at galactic halo) in late 2017. [7] RADES detector attached to this haloscope has a 1 m long alternating-irises stainless-steel cavity able to search for dark matter axions around . Further prospects of improving the detector system with enhancements such as superconductive cavities and ferro-magnetic tunings are being looked into. [16] [7]

KWISP detector

KWISP at CAST is designed to detect the coupling of solar chameleons with matter particles. It uses a very sensitive optomechanical force sensor, capable of detecting a displacement in a thin membrane caused by the mechanical effects from the solar chameleon interactions. [17] [18] [8]

CAST-CAPP

This detector has a delicate tuning mechanism, made of 2 parallel sapphire plates and activated by a piezoelectric motor. The maximum tuning corresponds to axions masses between 21–23 μeV. CAST-CAPP detector is also sensitive to dark matter axion tidal or cosmological streams and to the theorized axion mini-clusters. A newer and better version of CAPP is being developed at CAPP, South Korea. [19] [8] [20]

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. [21] [22] In the initial run period, the first three CAST detectors put an upper limit of  on (parameter for axion-photon coupling) with a 95% confidence limit (CL) for axion mass- . [23] For axion mass range between and , RADES constrained the axion-photon coupling constant with just about 5% error. [7] The most recent results, in 2017 set an upper limit on (with 95% CL) for all axions with masses below 0.02 eV. [4] [24] CAST has thus improved the previous astrophysical limits and has probed numerous relevant axion models of sub-electron-volt mass. [25]

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, . [26] [8] The new detectors at CAST are also looking for proposed dark matter candidates such as the solar chameleons and pharaphotons as well as the relic axions from the Big bang and Inflation. [26] [27] 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'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 flares, for which the CAST haloscope will serve as a testbed. [28] [29] [30]

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. [31] Using the GridPix detector, the upper bound on the chameleon photon coupling constant- was determined to be equal to for (chameleon matter coupling constant) in the range of 1 to . [14] KWISP detector obtained an upper limit on the force acting on its detector membrane due to chameleons as pNewton, which corresponds to a specific exclusion zone in - plane and complements the results obtained by GridPix. [17] [32]

Related Research Articles

In astronomy, dark matter is a hypothetical form of matter that appears not to interact with light or the electromagnetic field. Dark matter is implied by gravitational effects which cannot be explained by general relativity unless more matter is present than can be seen. Such effects occur in the context of formation and evolution of galaxies, gravitational lensing, the observable universe's current structure, mass position in galactic collisions, the motion of galaxies within galaxy clusters, and cosmic microwave background anisotropies.

<span class="mw-page-title-main">Neutrino</span> Elementary particle with extremely low mass

A neutrino is a fermion that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was long thought to be zero. The rest mass of the neutrino is much smaller than that of the other known elementary particles. The weak force has a very short range, the gravitational interaction is extremely weak due to the very small mass of the neutrino, and neutrinos do not participate in the electromagnetic interaction or the strong interaction. Thus, neutrinos typically pass through normal matter unimpeded and undetected.

Weakly interacting massive particles (WIMPs) are hypothetical particles that are one of the proposed candidates for dark matter.

<span class="mw-page-title-main">Standard Model</span> Theory of forces and subatomic particles

The Standard Model of particle physics is the theory describing three of the four known fundamental forces in the universe and classifying all known elementary particles. It was developed in stages throughout the latter half of the 20th century, through the work of many scientists worldwide, with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks. Since then, proof of the top quark (1995), the tau neutrino (2000), and the Higgs boson (2012) have added further credence to the Standard Model. In addition, the Standard Model has predicted various properties of weak neutral currents and the W and Z bosons with great accuracy.

In supersymmetry, the neutralino is a hypothetical particle. In the Minimal Supersymmetric Standard Model (MSSM), a popular model of realization of supersymmetry at a low energy, there are four neutralinos that are fermions and are electrically neutral, the lightest of which is stable in an R-parity conserved scenario of MSSM. They are typically labeled
N͂0
1,
N͂0
2,
N͂0
3 and
N͂0
4 although sometimes is also used when is used to refer to charginos.

An axion is a hypothetical elementary particle originally postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics (QCD). If axions exist and have low mass within a specific range, they are of interest as a possible component of cold dark matter.

<span class="mw-page-title-main">Fermi Gamma-ray Space Telescope</span> Space telescope for gamma-ray astronomy launched in 2008

The Fermi Gamma-ray Space Telescope, formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor, is being used to study gamma-ray bursts and solar flares.

<span class="mw-page-title-main">Neutrino astronomy</span> Observing low-mass stellar particles

Neutrino astronomy is the branch of astronomy that observes astronomical objects with neutrino detectors in special observatories. Neutrinos are created as a result of certain types of radioactive decay, nuclear reactions such as those that take place in the Sun or high energy astrophysical phenomena, in nuclear reactors, or when cosmic rays hit atoms in the atmosphere. Neutrinos rarely interact with matter, meaning that it is unlikely for them to scatter along their trajectory, unlike photons. Therefore, neutrinos offer a unique opportunity to observe processes that are inaccessible to optical telescopes, such as reactions in the Sun's core. Neutrinos can also offer a very strong pointing direction compared to charged particle cosmic rays.

<span class="mw-page-title-main">LHCb experiment</span> Experiment at the Large Hadron Collider

The LHCb experiment is a particle physics detector experiment collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designed primarily to measure the parameters of CP violation in the interactions of b-hadrons. Such studies can help to explain the matter-antimatter asymmetry of the Universe. The detector is also able to perform measurements of production cross sections, exotic hadron spectroscopy, charm physics and electroweak physics in the forward region. The LHCb collaboration, who built, operate and analyse data from the experiment, is composed of approximately 1260 people from 74 scientific institutes, representing 16 countries. Chris Parkes succeeded on July 1, 2020 as spokesperson for the collaboration from Giovanni Passaleva. The experiment is located at point 8 on the LHC tunnel close to Ferney-Voltaire, France just over the border from Geneva. The (small) MoEDAL experiment shares the same cavern.

<span class="mw-page-title-main">Two-photon physics</span> Branch of particle physics concerning interactions between two photons

Two-photon physics, also called gamma–gamma physics, is a branch of particle physics that describes the interactions between two photons. Normally, beams of light pass through each other unperturbed. Inside an optical material, and if the intensity of the beams is high enough, the beams may affect each other through a variety of non-linear effects. In pure vacuum, some weak scattering of light by light exists as well. Also, above some threshold of this center-of-mass energy of the system of the two photons, matter can be created.

Sterile neutrinos are hypothetical particles that interact only via gravity and not via any of the other fundamental interactions of the Standard Model. The term sterile neutrino is used to distinguish them from the known, ordinary active neutrinos in the Standard Model, which carry an isospin charge of ±+1/ 2  and engage in the weak interaction. The term typically refers to neutrinos with right-handed chirality, which may be inserted into the Standard Model. Particles that possess the quantum numbers of sterile neutrinos and masses great enough such that they do not interfere with the current theory of Big Bang nucleosynthesis are often called neutral heavy leptons (NHLs) or heavy neutral leptons (HNLs).

<span class="mw-page-title-main">IceCube Neutrino Observatory</span> Neutrino detector at the South Pole

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The chameleon is a hypothetical scalar particle that couples to matter more weakly than gravity, postulated as a dark energy candidate. Due to a non-linear self-interaction, it has a variable effective mass which is an increasing function of the ambient energy density—as a result, the range of the force mediated by the particle is predicted to be very small in regions of high density but much larger in low-density intergalactic regions: out in the cosmos chameleon models permit a range of up to several thousand parsecs. As a result of this variable mass, the hypothetical fifth force mediated by the chameleon is able to evade current constraints on equivalence principle violation derived from terrestrial experiments even if it couples to matter with a strength equal or greater than that of gravity. Although this property would allow the chameleon to drive the currently observed acceleration of the universe's expansion, it also makes it very difficult to test for experimentally.

<span class="mw-page-title-main">NA62 experiment</span>

The NA62 experiment is a fixed-target particle physics experiment in the North Area of the SPS accelerator at CERN. The experiment was approved in February 2007. Data taking began in 2015, and the experiment is expected to become the first in the world to probe the decays of the charged kaon with probabilities down to 10−12. The experiment's spokesperson is Cristina Lazzeroni. The collaboration involves 333 individuals from 30 institutions and 13 countries around the world.

<span class="mw-page-title-main">Dark photon</span> Hypothetical force carrier particle connected to dark matter

The dark photon is a hypothetical hidden sector particle, proposed as a force carrier similar to the photon of electromagnetism but potentially connected to dark matter. In a minimal scenario, this new force can be introduced by extending the gauge group of the Standard Model of Particle Physics with a new abelian U(1) gauge symmetry. The corresponding new spin-1 gauge boson can then couple very weakly to electrically charged particles through kinetic mixing with the ordinary photon and could thus be detected. The dark photon can also interact with the Standard Model if some of the fermions are charged under the new abelian group. The possible charging arrangements are restricted by a number of consistency requirements such as anomaly cancellation and constraints coming from Yukawa matrices.

<span class="mw-page-title-main">Luigi Di Lella</span> Italian experimental particle physicist

Luigi Di Lella is an Italian experimental particle physicist. He has been a staff member at CERN for over 40 years, and has played an important role in major experiments at CERN such as CAST and UA2. From 1986 to 1990 he acted as spokesperson for the UA2 Collaboration, which, together with the UA1 Collaboration, discovered the W and Z bosons in 1983.

<span class="mw-page-title-main">FASER experiment</span> 2022 particle physics experiment at the Large Hadron Collider at CERN

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<span class="mw-page-title-main">NA64 experiment</span>

NA64 experiment is one of the several experiments at CERN's Super Proton Synchrotron (SPS) particle collider searching for dark sector particles. It is a fixed target experiment in which an electron beam of energy between 100-150 GeV, strikes fixed atomic nuclei. The primary goal of NA64 is to find unknown and hypothetical particles such as dark photons, axions, and axion-like particles.

<span class="mw-page-title-main">International Axion Observatory</span> Axion helioscope

The International Axion Observatory (IAXO) is a next-generation axion helioscope for the search of solar axions and axion-like particles. It is the follow-up of the CERN Axion Solar Telescope (CAST), which has been operating since 2003. The IAXO will be set up by implementing the helioscope concept used in the CAST experiment to its largest possible size.

References

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  23. ↑ CAST Collaboration (2007-04-17). "An improved limit on the axion-photon coupling from the CAST experiment". Journal of Cosmology and Astroparticle Physics. 2007 (4): 010. arXiv: hep-ex/0702006 . Bibcode:2007JCAP...04..010A. doi:10.1088/1475-7516/2007/04/010. ISSN   1475-7516. S2CID   119067481.
  24. ↑ "CAST: from Solar to Dark Matter Axions searches". EP News. Retrieved 2021-06-23.
  25. ↑ "BabyIAXO submits for publication its Conceptual Design Report". EP News. Retrieved 2021-06-23.
  26. 1 2 "CAST in Time – The Quest for Axions and Chameleons". EP News. Retrieved 2021-06-23.
  27. ↑ "CAST opens a new window into dark energy and dark matter after 11 years of operation and continuous renewal". EP News. Retrieved 2021-06-23.
  28. ↑ "OSQAR experiment sheds light on a hidden sector of CERN's scientific heritage". EP News. Retrieved 2021-06-23.
  29. ↑ "Search for axions in streaming dark matter". EP News. Retrieved 2021-06-23.
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  31. ↑ "Colliders join the hunt for dark energy". CERN Courier. 2019-01-24. Retrieved 2021-06-23.
  32. ↑ "KWISP detector searches for dark energy from the Sun". CERN. Retrieved 2021-06-23.
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