In a lab in Illinois, physicists captured and tamed a tiny particle of antimatter in a trap with invisible walls. By studying how the positron behaved as time goes by, the researchers may soon have a chance to break our best mathematical model of physical reality. The positron is the antimatter counterpart of the electron, which means the two particles have the same mass but the opposite electric charge.
Unlike electrons, however, positrons are rare and typically exist for a tiny fraction of a second because the moment one meets one of the super-abundant electrons in our universe, the pair annihilate. This makes positrons difficult to study. Gerald Gabrielse at Northwestern University in Illinois and his colleagues have now found a way to trap a positron and keep it around for months on end.
By analysing data collected while the positron was trapped, they plan to precisely measure the antiparticle’s properties and consequently investigate one of the biggest problems with the standard model of particle physics. The researchers obtained the positron from a radioactive isotope of sodium that emits one whenever it decays. Such positrons are very fast and hard to control, so they placed the sodium into a special refrigerator to lower its temperature and energy, and slow down the antiparticles.
They slowed them further by directing the positrons through a tungsten crystal. While some positrons were annihilated as they travelled through the crystal, some came through unscathed. They were then directed into a refrigerated chamber that was empty of all other particles.
Here, electronic components generated electromagnetic fields that confined a single incoming positron, serving as invisible walls that trapped the particle. The researchers then pushed the positron into its lowest possible energy state, which Gabrielse says allowed them to keep the otherwise elusive antiparticle trapped for months. They could also push it into the next lowest energy state with controlled bursts of microwaves.
How much more fundamental, how much neater can it get?” he says. The payoff for trapping and controlling the positron despite these experimental challenges could be remarkable. Specifically, Gabrielse and his colleagues want to measure the positron’s magnetic moment, which is a number that quantifies its response to magnetic fields.
Extract — continue reading at the source.
