Physicists Hold a Single Antimatter Particle for Months to Study Its Properties
Researchers at Northwestern University in the US kept a single positron, the antimatter counterpart of the electron, trapped for months. This allows repeated measurements and a more precise search for possible differences between matter and antimatter.
A team of physicists at Northwestern University in the United States has kept a single antimatter particle, a positron, trapped for months. The positron is the antimatter counterpart of the electron. The particle was cooled to a temperature near absolute zero, which let the researchers control its quantum states with great precision without touching it. The results were published in Physical Review Letters and bear on one of physics' big open questions: why the universe is dominated by ordinary matter.
Why antimatter is hard to study
Mathematics predicts that every matter particle has a matching antiparticle, and scientists have confirmed this experimentally. In theory, the universe should therefore contain similar amounts of both, yet nearly everything we observe is ordinary matter. The reason is still unknown.
Antimatter can be produced in laboratories, but studying it is difficult. When an antiparticle meets ordinary matter, the two annihilate and release energy. To prevent this, scientists use vacuum chambers and electromagnetic fields that hold antiparticles in isolation. Even so, examining their behavior at the quantum scale remains challenging.
How the new device works
The team, led by Gerald Gabrielse, built a device called a single-positron quantum cyclotron. It uses electric and magnetic fields to hold the positron in a vacuum at a temperature close to absolute zero. The particle is thus in its lowest energy state, so the researchers can induce controlled changes in its quantum behavior. Unlike other particle physics methods, this approach does not destroy the particle, so it could be kept for months and measurements could be repeated.
What it could reveal
Matter and antimatter are known to have very similar properties. An electron and a positron, for example, have exactly the same mass but opposite electric charges. Still, it is unclear just how similar they are, or whether small differences have gone unnoticed in experiments so far. The researchers want to compare the magnetic properties of the two particles. Electrons have already been measured with great precision, but matching that precision for positrons has been harder. According to the American Physical Society, the new device could allow antimatter measurements about 30 times more precise than before.
So far, the experiment has not revealed any unexpected differences between the two particles. It has improved the ability to detect such differences. If future measurements show that a positron responds to magnetic fields differently from an electron, scientists would need to revise some of the laws used to explain the behavior of matter and antimatter.
