📦 A package filled... with antimatter

An experiment has managed to transport antiprotons by truck from one end to the other of CERN's main site, an essential first step towards delivering antimatter to other laboratories in Europe.

The team of the BASE experiment at CERN has succeeded in maintaining a cloud of 92 antiprotons in an innovative device, a portable cryogenic Penning trap, then disconnecting the device from the facility, loading it into a truck, and continuing the experiment after this transport operation. This is a real feat: antimatter is very difficult to preserve, as it annihilates upon contact with matter.


This world first is a test, with the ultimate goal of transporting antiprotons to other laboratories in Europe, such as Heinrich-Heine University in Düsseldorf (HHU), where very high-precision measurements of antimatter properties could be made.

Antimatter particles are a category of particles found in nature, almost identical to ordinary matter particles, but with reversed charges and magnetic moments. According to the laws of physics, matter and antimatter must have been created in equal amounts during the Big Bang. Particles and antiparticles should have quickly annihilated each other, leaving behind an empty Universe.


Yet, the Universe contains mostly matter: this asymmetry has intrigued scientists for decades, making them suspect that invisible differences exist which could explain why matter remained, while antimatter almost entirely disappeared.

To better understand antimatter, the BASE experiment aims to precisely measure the properties of antiprotons, such as their intrinsic magnetic moment, in order to then compare these measurements with those of protons. But it faces a difficulty: "The machines and equipment at the antimatter factory, where the BASE experiment is located, generate magnetic field fluctuations that limit measurement accuracy, explains Stefan Ulmer, spokesperson for the BASE experiment.


"These fluctuations are tiny, on the order of a nanotesla, 20,000 times weaker than Earth's magnetic field; they cannot be detected outside the building. However, given the extreme precision of the measurements made by the BASE experiment to achieve a finer understanding of the fundamental properties of antiprotons, we need to take the experiment out of the building," explains Stefan Ulmer.

CERN's antimatter factory is the only place in the world where antiprotons can be produced, stored, and studied. Two successive decelerators, the Antiproton Decelerator (AD) and the Extra Low Energy Antiproton ring (ELENA), deliver low-energy antiprotons to several experiments: the lower their energy, the easier they are to store and study.

The BASE experiment, which holds the record for antiproton storage (over a year), invented an innovative method to move to the next stage: transporting antiprotons in a self-contained space, away from the beamline, to enable more precise research and to benefit other teams. That is why it developed the BASE-STEP, trap, designed to store and transport antiprotons.

"The goal of the BASE-STEP device is to trap antiprotons and deliver them to our precision laboratories, in specific spaces at CERN, at Heinrich-Heine University in Düsseldorf, at Leibniz University in Hanover, and perhaps to other laboratories capable of performing very high-precision measurements on antiprotons, which unfortunately is not possible at the antimatter factory," explains Christian Smorra, head of the BASE-STEP project. "We validated the feasibility of the project with protons last year, but what we have accomplished today with antiprotons is a huge step forward towards achieving our goal."

The BASE-STEP trap is small enough to be loaded onto a truck and pass through standard laboratory doors; it is also capable of withstanding shocks and vibrations during transport. The current device, which includes a superconducting magnet, a liquid helium cryogenic cooling system, power sources, and a vacuum chamber that traps antiparticles using magnetic and electric fields, weighs 1,000 kg (approximately 2,205 pounds): it is therefore much more compact than the BASE device or any other system used to study antimatter.

"Getting to our first destination, our precision laboratory at Heinrich-Heine University in Germany, would take at least eight hours," continues Christian Smorra. "This means the trap's superconducting magnet will have to stay at a temperature below 8.2 kelvins the entire time. So, in addition to liquid helium, we would need a generator to power a cryogenic refrigerator in the truck. We are currently studying the possibilities." Regardless, the biggest challenge lies upon arrival: transferring the antiprotons to the experiment without them disappearing.

"Transporting antimatter is an innovative and ambitious undertaking, and I congratulate the BASE collaboration on this remarkable achievement. We are at the beginning of a fantastic scientific adventure that will allow us to deepen our knowledge of antimatter," concludes Gautier Hamel de Monchenault, Director of Research and Scientific Computing at CERN.