IAXO: Search for Axions

 Axions are promising candidates for dark matter and thus might play an important role in the Standard Model. The search will be intensified by the largest axion helioscope experiment planned up to now, IAXO - the International Axion Observatory. It is suited to investigate unexplored parameter regions of the axion as well as other undiscovered cosmological particles.


The axion is a hypothetical particle that was introduced in 1977 to solve the strong CP problem of the Standard Model. It is also a candidate for light dark matter, due to its very weak interaction strength and its low mass.

The figure on the right hand side shows several possible interactions of the axion with known matter, with the prima coffin effect in the upper left being the one exploited by helioscope experiments such as IAXO. The other interactions are other examples of how axions can potentially be produced in celestial bodies like the Sun, depending on their coupling strengths to photons or electrons.
The constraints on these coupling strengths, as well as the mass of the axion, have been established over the years in various experiments as well as by the physical limits of our universe.

Axion Interactions
© Javier Redondo
Eine Wissenschaftlerin und ein Wissenschaftler arbeiten hinter einer Glasfassade und mischen Chemikalien mit Großgeräten.
© IAXO Collaboration


Helioscopes experiments are based on the idea that the core of the Sun is so energetic that the production of axions can be induced by various mechanisms. On Earth, a magnet is then pointed at the Sun, in which axions couple to a photon via the Primakoff effect. These X-ray photons retain the direction and energy of the axions, making them focusable with a suitable telescope. The telescope is followed by a detector which should be able to measure photons in the energy range from 0.1 keV to about 10 keV.


With a magnet length of 20 m and 8 possible measurement sites, IAXO is the largest helioscope experiment planned so far in the search for axions and ALPs (Axion Like Particles). Each of these measuring stations can be equipped with different telescopes and detectors, which should cover a wide range of axion parameters. A movable platform allows the magnet to track the Sun for about 12 hours of the day, with the other 12 hours being important for subsurface measurements.

As follow-up experiment of the long-operating CAST helioscope, IAXO is designed to search for the axion in unprecedented parameter regions. Because of its size and the novelty of many of its components, such as the platform, BabyIAXO was planned as a pre-experiment.

© IAXO Collaboration
Eine Wissenschaftlerin und ein Wissenschaftler arbeiten hinter einer Glasfassade und mischen Chemikalien mit Großgeräten.
© IAXO Collaboration


To test the technology which will be used in IAXO and to search for the axion itself, BabyIAXO will be built at DESY in Hamburg. In one of the detector halls of the former accelerator Hera, the setup, depicted at the left hand side, is planned.

BabyIAXO shall consist of a 10m long magnet, which tracks the sun through a movable platform 12 hours a day. Because of the two planned cylindrical holes in the magnet, two superstructures can be mounted behind it. One of the two setups is planned with an X-ray telescope from the XMM-Newton mission, which will focus the photons after 7.5 m. The other setup is planned with a prototype X-ray telescope from the XMM-Newton mission. The other setup is planned to be equipped with a prototype from a planned IAXO telescope. Various detectors are being built by subgroups of the IAXO Collaboration to detect the X-ray photon signal. The GridPix detector, which we are developing and manufacturing in our group, is presented below.

GridPix Detector

After the successful operation of several GridPix based detectors at the CAST experiment, we are now planning to build one for BabyIAXO. The requirements here are similar as before: The X-ray photons have to pass through a vacuum-tight window into the gas volume, and as few of them as possible should be absorbed. In the gas volume they then release electrons, which move towards the chip through an applied electric field. Shortly before they reach the chip, they will be accelerated even more with the aid of a grating structure in order to amplify the signal.

A big difference to previous detectors is a new chip as well as even less background radiation by the detector material. Therefore, the detector shown on the right is planned with radioactive pure copper and Teflon, as well as the readout electronics remote from the detector body. A first prototype is already being tested.

© Schiffer / Universität Bonn

Further Links

More information can be found on the right. On the official website of IAXO you can find more papers under "publications and presentations", for example the conceptual design, which describes the structure and the physics behind it in more detail. To learn more about axions and especially their interactions with particles other than photons, you can follow the axion theory link.


Avatar Desch

Prof. Dr. Klaus Desch


Nußallee 12

53115 Bonn

+49 228 73 3236

Avatar Kaminski

Dr. Jochen Kaminski


Kreuzbergweg 24

53115 Bonn

+49 228 73 60070

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