Overnight Anti-Hydrogen’s New Dawn: ALPHA’s Cooling Breakthrough

Scientists at CERN have transformed the dream of obtaining tens of thousands of anti-hydrogen atoms from a years-long aspiration into a routine overnight task. Participants of the ALPHA experiment presented a new cooling technology that allows the generation of more than 15,000 anti-hydrogen atoms in just a few hours. This marks a significant leap in obtaining the simplest form of antimatter atoms.

To create anti-hydrogen, the team must first capture and cool clouds of positrons and antiprotons separately before combining them. Over the years, this process has been continually refined. The latest breakthrough-an innovative method of cooling positrons-has increased the production rate of anti-hydrogen by 8 times.

The essence of this achievement lies in the way positrons are prepared. Initially, particles are generated from a radioactive form of sodium and captured inside a Penning trap, where electromagnetic fields keep them in place. Inside the trap, they naturally spin, losing a bit of energy as they move. This self-cooling effect helps but is insufficient for efficient anti-hydrogen formation.

To overcome this limitation, the ALPHA group introduced a cloud of laser-cooled beryllium ions into the trap, allowing positrons to shed energy through a process known as sympathetic cooling. This method, in which one group of particles is cooled through interaction with another already-cooled group, allowed the positron cloud to be cooled to temperatures around −266 °C. At such low energies, particles are more likely to bind with antiprotons to form anti-hydrogen.

As a result, more than 15,000 anti-hydrogen atoms were produced in less than 7 hours. For comparison, a previous experiment required 10 weeks to collect about 16,000 atoms for high-precision spectroscopic study.

“The new technique radically changes the landscape when it comes to studying systematic uncertainties in our measurements. We can now accumulate anti-hydrogen overnight and measure the spectral line the next day,” said Niels Madsen, deputy representative of ALPHA and leader of the positron cooling project.

In the experimental series of 2023–2024, this method allowed for the production of over two million anti-hydrogen atoms, achieving results previously thought impossible. This year, the ALPHA collaboration is using this unprecedented supply to study the gravitational effects on antimatter as part of the ALPHA-g experiment, a key test of fundamental physics.

As sympathetic cooling continues to unlock larger data sets and faster measurements, scientists expect to explore the properties of antimatter with unparalleled precision. This could deepen the understanding of asymmetries in the universe.