The possibility of the presence of dark matter has been dramatically narrowed by an international research team using a precision experiment created at the University of Bern. The experiment, which was conducted at the European Research Neutron Source at the Institute Laue-Langevin in France, significantly advances our understanding of these as-yet-unidentified particles.
Cosmological studies of star and galaxy orbits can yield clear conclusions about the alluring gravitational forces that act between celestial bodies.The startling discovery is that observable matter is far from sufficient to explain how galaxies form or travel. This implies the existence of a different kind of substance that is currently undiscovered. As a result, Fritz Zwicky, a Swiss physicist and astronomer, postulated the presence of what is now known as “dark matter” in the year 1933. Approximately five times as massive as the matter we are familiar with, dark matter is a kind of substance that isn’t clearly observable but interacts through gravity.
A recent precision experiment created at the University of Bern’s Albert Einstein Center for Fundamental Physics (AEC) allowed an international research team to drastically reduce the possibility that dark matter exists. The AEC is one of the top international research organizations in the area of particle physics, with more than 100 members. The team led by Bern has now published its findings in the academic journal Physical Review Letters.
The mystery surrounding dark matter
Lead author of the study and PhD candidate at the AEC, Ivo Schulthess, said, “What dark matter is actually constituted of is still absolutely uncertain.” The fact that it is not composed of the same materials as the stars, the planet Earth, or us humans, however, is unquestionable. Globally, increasingly sensitive techniques and tests are being utilized to look for potential dark matter particles, but so far without results.
Axions are a promising class of potential candidates for dark matter particles. They are hypothetical elementary particles. These incredibly light particles have the potential to simultaneously explain other significant particle physics events that are still poorly understood, which is a significant advantage.
Bern experiment sheds light on the darkness
For the Beam EDM experiment, which was developed by Florian Piegsa, a professor of low energy and precision physics at the AEC and recipient of one of the prestigious ERC Starting Grants from the European Research Council in 2016 for his work with neutrons, “our team has succeeded in designing and building an extremely sensitive measurement apparatus thanks to many years of expertise,” says Piegsa. If the mysterious axion is real, it ought to leave a distinctive mark on the measurement tool.
As neutron spins move through a superposition of electric and magnetic fields, “this experiment allows us to estimate the rotational frequency of neutron spins,” says Schulthess. Each neutron’s spin functions as a form of compass needle, rotating in a magnetic field much faster than the second hand of a watch (almost 400,000 times faster). In order to look for the smallest periodic changes that would be brought on by interactions with the axions, Piegsa and his team carefully measured this rotational frequency. The experiment’s findings were unmistakable. According to Piegsa, “the neutrons’ rotational frequency remained unchanged, indicating that there is no evidence of axions in our measurement.”
Parameter space successfully narrowed down
The measurements, which were made at the European Research Neutron Source at the Institute Laue-Langevin in collaboration with researchers from France, allowed for the experimental exclusion of an as-yet fully unknown parameter space of axions. Additionally, it demonstrated that it was feasible to look for fictitious axion that would be 1,000 times heavier than those that could previously be found in prior studies.
Although the existence of these particles is still unknown, Schulthess says, “We have effectively excluded an important parameter space of dark matter.” This work can now be built upon in later experiments. We would gain significant insight into nature’s fundamentals and move closer to a full understanding of the universe if we could finally resolve the mystery of dark matter, says Piegsa.
The European Research Council and the Swiss National Science Foundation provided funding for the experiment.
