The x-ray telescope of CAST

Kuster, M.; Bräuninger, H.; Cebrián, S.; Davenport, M.; Eleftheriadis, C.; Englhauser, J.; Fischer, H.; Franz, J.; Friedrich, Péter; Hartmann, R.; Heinsius, F. H.; Hoffmann, D. H. H.; Hoffmeister, G.; Joux, J. N.; Kang, D.; Königsmann, K.; Kotthaus, R.; Papaevangelou, T.; Lasseur, C.; Lippitsch, A.; Lütz, G.; Morales, J.; Rodríguez, A. Soto; Strüder, L.; Vogel, Julia K.; Zioutas,

doi:10.1088/1367-2630/9/6/169

Cited by 63 publications

(73 citation statements)

References 24 publications

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“…During this long experimental programme, CAST has used a variety of detection systems at both magnet ends, including a multiwire time projection chamber 25 , several Micromegas detectors 26 , a low-noise charged coupled device attached to a spare X-ray telescope (XRT) from the ABRIXAS X-ray mission 27 , a γ -ray calorimeter 21 , and a silicon drift detector 23 .…”

mentioning

confidence: 99%

New CAST limit on the axion–photon interaction

2017

Nature Phys

875

709

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Hypothetical low-mass particles, such as axions, provide a compelling explanation for the dark matter in the universe. Such particles are expected to emerge abundantly from the hot interior of stars. To test this prediction, the CERN Axion Solar Telescope (CAST) uses a 9 T refurbished Large Hadron Collider test magnet directed towards the Sun. In the strong magnetic field, solar axions can be converted to X-ray photons which can be recorded by X-ray detectors. In the 2013-2015 run, thanks to low-background detectors and a new X-ray telescope, the signal-to-noise ratio was increased by about a factor of three. Here, we report the best limit on the axion-photon coupling strength (0.66 × 10 −10 GeV −1 at 95% confidence level) set by CAST, which now reaches similar levels to the most restrictive astrophysical bounds.A dvancing the low-energy frontier is a key endeavour in the worldwide quest for particle physics beyond the standard model and in the effort to identify dark matter 1,2 . Nearly massless pseudoscalar bosons, often generically called axions, are particularly promising because they appear in many extensions of the standard model. They can be dark matter in the form of classical field oscillations that were excited in the early universe, notably by the re-alignment mechanism 3 . One particularly well motivated case is the quantum chromodynamics (QCD) axion, the eponym for all such particles. The existence of this new lowmass boson follows from the Peccei-Quinn mechanism as an explanation why QCD is perfectly time-reversal invariant within current experimental precision 3 .Axions were often termed 'invisible' because of their extremely feeble interactions, yet they are the target of a fast-growing international landscape of experiments. Numerous existing and foreseen projects assume that axions are the galactic dark matter and use a variety of techniques that are sensitive to different interaction channels and optimal in different mass ranges 4 . Independently of the dark-matter assumption, one can search for new forces mediated by these low-mass bosons 5 or the back-reaction on spinning black holes (superradiance) 6 . Stellar energy-loss arguments provide restrictive limits that can guide experimental efforts, and in some cases may even suggest new loss channels 3,7,8 .The least model-dependent search strategies use the production and detection of axions and similar particles by their generic twophoton coupling. It is given by the vertex L aγ = −(1/4) g aγ F µν F µν a = g aγ E · B a, where a is the axion field, F the electromagnetic field-strength tensor, and g aγ a coupling constant of dimension (energy) −1 . Notice that we use natural units with = c = k B = 1. This vertex enables the decay a → γ γ , the Primakoff production in stars-that is, the γ → a scattering in the Coulomb fields of charged particles in the stellar plasma-and the coherent conversion a ↔ γ in laboratory or astrophysical B-fields 9,10 .The helioscope concept, in particular, uses a dipole magnet directed at the Sun to convert axions to...

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confidence: 99%

New CAST limit on the axion–photon interaction

2017

Nature Phys

875

709

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“…The maximum magnetic field that can be achieved with this prototype magnet is ≈ 9 T. The magnet is mounted on an azimuthal moving platform that allows to track the Sun for 1.5 h (±8 • in height and ≈ 100 • in azimuth) during sunrise and sunset. To detect the axions, three different types of detectors are attached to the ends of the magnet pipes: a gaseous detector with a novel MICROMEGAS readout (15) and an X-ray telescope with a pn-CCD chip as focal plane detector (16) to detect axions during sunrise, and a Time Projection Chamber (TPC) which covers the opposite end of the magnet pipes, ready to collect axions during sunset (17). CAST has taken data with the conversion region being evacuated during the years 2003 and 2004.…”

Section: Helioscope Implementationsmentioning

confidence: 99%

Axion Searches in the Past, at Present, and in the Near Future

Battesti

Beltrán

Davoudias

et al.

Lecture Notes in Physics

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Summary. Theoretical axion models state that axions are very weakly interacting particles. In order to experimentally detect them, the use of colorful and inspired techniques becomes mandatory. There is a wide variety of experimental approaches that were developed during the last 30 years, most of them make use of the Primakoff effect, by which axions convert into photons in the presence of an electromagnetic field. We review the experimental techniques used to search for axions and will give an outlook on experiments planned for the near future.

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“…On both ends of the magnet X-ray detectors are mounted. Three out of four stations are equipped with microbulk Micromegas detectors and until mid of 2013 an X-ray telescope in combination with a pnCCD detector [7] was used at the fourth station.…”

Section: The Cern Axion Solar Telescopementioning

confidence: 99%

An InGrid based Low Energy X-ray Detector for the CAST Experiment

Krieger¹,

Desch²,

Kamiński³

et al. 2015

Proceedings of Technology and Instrumentation in Particle Physics 2014 — PoS(TIPP2014)

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The CERN Axion Solar Telescope (CAST) is searching for axions and other new particles like chameleons coupling to photons and emerging from the Sun. Those particles are converted into soft X-ray photons in a high magnetic field. To enhance sensitivity for physics beyond the Standard Model it is necessary to cope with weak couplings and low energies, thus requiring an efficient background discrimination as well as a detection threshold below 1 keV. A promising candidate for a future CAST detector is an InGrid based X-ray detector. This detector combines the high spatial resolution of a pixelized readout with a highly granular Micromegas gas amplification stage. Fabrication by photolithographic postprocessing techniques allows to match the amplification grid to the pixels. The high granularity facilitates the detection of single electrons which allows to determine the X-ray energy by electron counting. Additionally, rejection of background events mostly originating from cosmic rays is provided by an event shape analysis exploiting the high spatial resolution. In order to demonstrate its low detection threshold, an InGrid based detector was tested in the CAST Detector Lab where an X-ray generator for energies down to a few hundred eV is available.Results of these tests demonstrate the detector's ability to detect the carbon K-alpha line at 277 eV. The detector was mounted afterwards at the CAST experiment behind an X-ray telescope in order to take data during the 2014 run of CAST.

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The x-ray telescope of CAST

Cited by 63 publications

References 24 publications

New CAST limit on the axion–photon interaction

New CAST limit on the axion–photon interaction

Axion Searches in the Past, at Present, and in the Near Future

An InGrid based Low Energy X-ray Detector for the CAST Experiment

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