Quick Takeaways
- Northwestern physicists trapped a single positron for months in an ultracold vacuum.
- A tungsten crystal slowed radioactive positrons before a Penning trap isolated them.
- Researchers controlled positron quantum states, enabling precise measurements without disturbing them.
- Measurements will test CPT symmetry and may illuminate why matter dominates antimatter.
Physicists Keep a Single Antimatter Particle Trapped for Months
A difficult particle to capture
Antimatter is hard to study because it vanishes when it meets ordinary matter. A positron—the antimatter counterpart of an electron—can be held in an electromagnetic trap, but first researchers must slow it enough to capture it.
A Northwestern University team used radioactive sodium to produce positrons, then sent them through a tungsten crystal. Most were lost, but some slowed down and emerged briefly paired with electrons as positronium. The researchers guided that short-lived state into a Penning trap, where electric and magnetic fields separated and confined the positron.
The trap operates in an ultra-high vacuum at 300 millikelvins, just above absolute zero. There, the team kept one positron for months and controlled its motion, measuring changes in its energy and spin without disrupting the particle.
Precision with a narrow purpose
The achievement is a research tool, not a practical way to store large amounts of antimatter. It depends on radioactive material, specialized cryogenic equipment, a powerful magnet and a carefully maintained vacuum. Capturing even one positron remains difficult.
Its scientific value could be substantial. The team plans to measure the positron’s magnetic moment and compare it with the electron’s. Under CPT symmetry, a core principle of physics, the two values should match in magnitude and have opposite signs. A precise match would strengthen a key prediction of the Standard Model; a difference could point to physics beyond it.
Either outcome would leave a major question unresolved: why the Universe contains far more matter than antimatter. The new trap will not answer that on its own, but it gives researchers a more precise way to test the rules that govern both.
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