Scientists Search for Axions, Unlocking the Secrets of Dark Matter

Scientists from the University of Oxford and their colleagues have conducted an experiment searching for hypothetical axion particles at the European X-Ray Free-Electron Laser (European XFEL) in Hamburg. The results of the study may bring scientists closer to solving the mystery of dark matter.

Axions are hypothetical particles proposed to solve a problem in particle physics: why neutrons, which consist of charged quarks, do not have an electric dipole moment. These tiny and light particles are thought to "compensate" for this imbalance. In addition, axions are considered a natural candidate for the role of dark matter - a mysterious substance that makes up most of the structure of the Universe.

To search for axions, scientists used the world's most powerful X-ray laser - the European XFEL. This facility includes a 3.4-kilometer tunnel with a superconducting linear accelerator and photon beams capable of generating ultrashort X-ray flashes at a frequency of 27,000 times per second.

The experiment was carried out using the "shining through walls" method. X-rays were directed through thin plates of precisely oriented germanium crystals with an intense internal electric field. For moving particles, this electric field looks like a strong magnetic field (about 1000 Tesla), which allows photons to turn into axions and back.

A titanium sheet was placed between the crystals, serving as a barrier for photons and allowing only the desired axions to pass through. These particles were then detected when they turned back into photons in a crystal on the other side.

Although axions were not found in this study, scientists have shown that their setup has sensitivity to axions, already comparable to other experiments at particle accelerators. This opens the way for future experiments, in which researchers will focus on axions in the mass range from milli- to kiloelectronvolts. They plan to improve sensitivity by several hundred times to be able to detect axions with properties predicted by the theory of quantum chromodynamics.

The lead author of the study, Dr. Jack Holliday from the UK Science and Technology Facilities Council (STFC), emphasized the versatility of XFEL technology in addressing the most complex questions of fundamental physics and expanding the boundaries of understanding the Universe.

Professor Gianluca Gregori, the principal investigator of the project, noted that this study was the culmination of many years of collaboration between various departments of the Department of Physics at the University of Oxford. He stressed that the experiment required complex interpretation of non-standard measurements, and it was thanks to the broad expertise of the united team that this task was successfully solved.

This study not only demonstrates the potential of new technologies in the study of fundamental questions of physics but also opens new horizons in the search for dark matter. Although axions have not yet been discovered, the experiment has significantly advanced the understanding of their search methods and laid the foundation for future, even more sensitive experiments.