About 80% of the matter in the universe is an undiscovered substance called "dark matter." Although its existence has been theorized for about 90 years, scientists from the JEDI collaboration are using advanced particle accelerator technology to develop new ways to detect it, although conclusive evidence remains elusive.
About 80% of the matter in the universe is an undiscovered substance called "dark matter." While the existence of dark matter has been theorized for about 90 years, scientists from the JEDI collaboration, using advanced particle accelerator technology, are developing new ways to detect it, although conclusive evidence remains elusive.
"This is the only way to reconcile the velocity distribution of visible matter within galaxies with the current knowledge that a previously unobserved form of 'dark' matter must additionally stabilize the galaxy," explains Jörg Pretz, one of the study's co-authors. He is also Deputy Director of the Institute of Nuclear Physics at the Urich Research Center and Professor at RWTH Aachen University
Physicists have been searching for this substance since the 1930s. There is no shortage of theories in the scientific community, but no one has yet successfully detected dark matter. Dr. Volker Hejny said: "This is because the nature of dark matter is still completely unclear."
Dr. Heini is also from the Jülich Institute for Nuclear Physics and, like his colleague Jörg Pretz, is a member of the international JEDI collaboration that carried out the experiment. JEDI is the abbreviation of Jülich Electric Dipolemoment Investigations. The scientists involved in the collaboration have been working on measuring the electric dipole moment of charged particles since 2011.
"Dark matter is invisible and has so far only manifested itself indirectly through its gravitational pull. Its influence is relatively small, which is why it is only in extremely massive cases - such as entire galaxies - that dark matter actually becomes apparent."
Theoretical physicists have proposed a number of hypothetical elementary particles that dark matter might be composed of. Depending on the properties of these particles, various methods can be used to detect them - methods that do not require highly sophisticated detection of gravitational effects. These methods include axions and axion-like particles.
In their experiments, the JEDI scientists took advantage of a special feature of the Jülich particle accelerator COSY: the use of polarized beams. Photo credit: Forschungszentrum Jülich/Ralf-Uwe Limbach
"Axions were originally developed to solve a problem in the strong interaction theory of quantum chromodynamics," explains Pretz. "The name axion dates back to Nobel Prize winner Frank Wilczek and refers to a brand of detergent: the particle exists to 'clean up' physics theory, so to speak."
To detect axions, scientists in the JEDI collaboration exploited the particle's spin. "Spin is a unique property of quantum mechanics that causes particles to behave like small bar magnets," Hejny explains. "For example, magnetic resonance imaging (MRI) in medical imaging takes advantage of this property. As part of this process, the spin of atomic nuclei is excited by strong external magnetic fields."
Magnetic resonance imaging has also been used to search for dark matter. In an ordinary MRI, atoms are at rest, while in an accelerator, particles move at almost the speed of light. This makes inspections in certain areas more sensitive and measurements more precise.
In their experiments, the JEDI scientists took advantage of a special feature of the Jülich particle accelerator COSY, which is the use of polarized beams. "In a conventional particle beam, the spin direction of the particles is random," Pretz said. "In a polarized particle beam, the spins are aligned in one direction." Only a few accelerators in the world have this capability. "
If, as scientists suspect, there is a background field of axions around us, then this will affect the motion of the spins - and thus may eventually be detected in experiments. However, the expected impact is minimal. The measurements are not precise enough. But while the JEDI experiment has yet to find evidence of dark matter particles, researchers have managed to further narrow down the possible interaction effects. Perhaps more importantly, they were able to establish a new and promising approach in the search for dark matter.