Figure 1: A researcher from the BASE collaboration monitoring the condition of 100 protons in a trap inside a unit (silver box on yellow trolley) before they are loaded onto a truck for transportation. © 2025 CERN/BASE/Julia Jäger
By taking around 100 protons for a spin in a truck, RIKEN researchers and others have demonstrated how antimatter particles could be transported for high-precision measurements in the future1.
Transporting antimatter particles is extremely challenging because if they momentarily come into contact with their real-matter counterparts, they will immediately annihilate each other in a puff of gamma rays and elementary particles. And it's very hard to prevent this because everything around us is made from normal matter.
Physicists are eager to discover why normal matter surrounds us when theory predicts that the Big Bang should have created an equal amount of antimatter.
Antimatter particles seem to be mirror-image versions of their real-matter counterparts, having identical mass but opposite charge. But if there were a tiny discrepancy between one of their properties, this could lead to the superabundance of matter that we observe today.
A spokesperson of the Baryon Antibaryon Symmetry Experiment (BASE) collaboration, Stefan Ulmer of the RIKEN Ulmer Fundamental Symmetries Laboratory, has dedicated his career to pursuing more accurate measurements on antiprotons to see if their properties differ ever so slightly from protons.
Despite having constructed the world's most sensitive detection systems and increased the accuracy of these measurements by a factor of thousands, his team has yet to find any differences.
Undeterred, Ulmer intends to keep going. "The technological challenge makes you more creative and inventive to try to push the limits to achieve higher and higher resolutions," he says.
One problem his team has encountered is their antiproton measurements have become so accurate that fluctuations in magnetic fields used to slow antiprotons at CERN now limit the accuracy of measurements.
"We've done world-record measurements on matter-antimatter symmetry," says Ulmer. "But our experiments have become so accurate that we cannot improve the results anymore in the background magnetic-field fluctuation produced by the accelerators at CERN."
To overcome this limitation, the team wants to transport antiprotons to a specially constructed low-noise laboratory. But that requires finding a way to move them while avoiding all contact with protons.
Now, they have taken a first step toward that goal by transporting protons in a trap for four hours around CERN on the French-Swiss border. About 100 protons were successfully transported without losing any of them.
The team eventually aims to transport antiprotons via autobahn to a specially designed lab in Dusseldorf, 800 kilometers away. If they can achieve that, they hope to enhance the accuracy of measurements by at least 100 fold.
"We intend to bring antiproton experiments to the ultimate limits," says Ulmer.
