Physicists trap a single antimatter particle for a month

Physicists have developed a way to hold one positron - the antimatter counterpart of an electron - in a trap for a month, long enough to investigate its quantum properties. Because antimatter annihilates when it contacts ordinary matter, the team had to slow the positrons and confine them without physical walls. They produced positrons by allowing radioactive sodium-22 to decay, then passed them through cold tungsten, where collisions drained energy from some particles. Electromagnetic fields guided the survivors into an ultracold vacuum, where electric and magnetic fields confined a lone positron. The researchers say the method could keep particles trapped indefinitely.

The advance makes possible a precise comparison of the positron’s magnetic moment with the electron’s. The team plans to measure the energies associated with changing the positron’s spin and moving it from its lowest energy state to the next one. A previous experiment measured the electron’s magnetic moment to one part in 10 trillion. The Standard Model predicts that the two particles’ magnetic moments should be exactly opposite; any mismatch would signal a failure of a fundamental symmetry in physics. Such a difference could also help explain why the early universe’s nearly equal quantities of matter and antimatter did not annihilate completely, leaving the matter that formed stars and planets.