Researchers from the University of Oxford, in collaboration with the UK Science and Technology Facilities Council (STFC) and several other laboratories, have recently achieved a significant milestone in the quest to understand dark matter through a groundbreaking experiment conducted at the European X-ray Free Electron Laser (European XFEL) Facility in Hamburg, Germany. This effort is outlined in a paper published in the prestigious journal “Physical Review Letters,” which offers a detailed exploration of the elusive particle known as the axion. This research not only sheds light on potential answers to longstanding physics conundrums but also deepens our understanding of the universe’s fundamental structure.

Axions are theoretical particles that arise from attempts to explain certain anomalies in particle physics, particularly why neutrons—composed of quarks—do not exhibit an electric dipole moment. In essence, the discovery of axions could provide critical evidence for new physics that goes beyond the Standard Model, the framework that currently governs our understanding of particle interactions. Their unique properties make them compelling candidates for dark matter, the mysterious substance that constitutes about 27% of the universe and remains undetectable by conventional means.

At the heart of this experiment is the European XFEL, regarded as the world’s largest and most powerful X-ray laser. This incredible facility possesses a 3.4-kilometer-long tunnel that houses a superconducting linear accelerator, capable of producing ultrashort X-ray flashes at an astonishing rate of 27,000 pulses per second. The sheer intensity and precision of these flashes allow researchers to investigate particle interactions in unprecedented detail, paving the way for innovations in a field that is often constrained by limitations in available technologies.

To conduct their search for axions, the researchers utilized thin slabs of precisely oriented germanium crystals, which are instrumental in the experiment due to