Physicists trap a single antimatter particle for a month

In a lab in Illinois, physicists managed to capture and contain a single positron, a type of antimatter, within a trap without walls. The positron, which has the same mass as an electron but an opposite electric charge, is typically short-lived and difficult to study due to the rapid annihilation that occurs when it meets electrons. To overcome these challenges, researchers Gerald Gabrielse and his team at Northwestern University devised a method to trap a positron for extended periods.

The team obtained the positron from a radioactive isotope of sodium, which emits positrons during decay. The positrons were then cooled and directed through a tungsten crystal, which further slowed them down. Some positrons were annihilated during this process, but others survived. These surviving positrons were guided into a chamber free of other particles, where electromagnetic fields created invisible walls that confined the single positron.

The researchers further controlled the positron's energy state, allowing it to be held in its lowest possible energy state for months. By pushing the positron into the next lowest energy state using controlled microwave bursts, the scientists could study its behavior more closely.

Trapping a positron is a formidable task, as any stray particle, light, or vibration could disturb the delicate balance required to maintain the trap. However, the potential rewards are significant. Measuring the positron's magnetic moment, a property that quantifies its response to magnetic fields, could provide the most precise comparison yet between matter and antimatter.

The standard model predicts that the magnetic moments of matter and antimatter should be identical, yet this prediction highlights a limitation in the current understanding of physics. By comparing the positron's magnetic moment with that of the electron, Gabrielse and his colleagues aim to uncover fundamental insights into the nature of the universe and potentially reveal new physics beyond the standard model.