On the hunt for axions
New X-ray experiment at the European XFEL could solve some of the mysteries of physics.
Researchers at European XFEL, together with colleagues from the UK Science and Technology Facilities Council (STFC), the University of Oxford and other research institutions, have been searching for a hypothetical particle that could potentially explain the dark matter of the universe. The experiment is described in a study published in Physical Review Letters.
The researchers hunted for so-called axions at the High Energy Density instrument HED/HiBEF at European XFEL. Axions are tiny and incredibly light hypothetical particles. They are intended to explain, for example, why neutrons, which make up atomic nuclei alongside protons, have no electric dipole moment, even though the nuclear building blocks consist of even smaller charged particles known as quarks. This could also be an indication of new physics beyond the standard model. Furthermore, axions are a natural candidate for dark matter, the mysterious substance that makes up most of the structure of the universe.
The researchers used European XFEL in Schenefeld near Hamburg, the largest and most powerful X-ray laser in the world for their experiments. They channelled the intense X-ray beam of European XFEL through thin plates of germanium crystals. These have strong electric fields inside. For moving particles, this appears like an extremely strong magnetic field of around 1000 Tesla. This enables photons to transform themselves into axions and back again.
A titanium foil inserted between the crystals acts as a barrier for the photons and only allows the sought-after axions to pass through. These would be detected when they convert back into photons in the crystal on the other side.
In this feasibility study, the researchers have shown that their setup can compete with experiments using particle accelerators in terms of sensitivity to axions. They are thus paving the way for experiments in which axions can be measured in the mass range from milli- to kiloelectronvolts. Their aim is to improve the sensitivity by a factor of several hundred in order to be able to detect axions predicted by the theory of quantum chromodynamics.
About European XFEL:
European XFEL in the Hamburg area is an international research facility of superlatives: 27,000 X-ray flashes per second and a brilliance that is a billion times higher than that of the best conventional X-ray sources open up new opportunities for science. Research groups from around the world are able to map the atomic details of viruses, decipher the molecular composition of cells, take three-dimensional “photos” of the nanoworld, “film” chemical reactions, and study processes such as those occurring deep inside planets.
The operation of the facility is entrusted to European XFEL, a non-profit company that cooperates closely with its main shareholder, the research centre DESY, and other organisations worldwide. European XFEL has a workforce of more than 550 employees. At present, 12 countries have signed the European XFEL convention: Denmark, France, Germany, Hungary, Italy, Poland, Russia, Slovakia, Spain, Sweden, Switzerland, and the United Kingdom. For more information on European XFEL go to https://www.xfel.eu.
Originalpublikation:
https://journals.aps.org/prl/accepted/2907fY5bF4913f8c79a96f53b9774fa2b8d729f2a (paper in Physical Review Letters: "Bounds on Heavy Axions with an X-Ray Free Electron Laser")
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