Northwestern team holds a single positron for months to test matter–antimatter differences

Mixed · 2Researchers at Northwestern University, led by Gerald Gabrielse, trapped a single positron, the antimatter counterpart of the electron, and kept it for months. 1 2 Mixed · 2The team built a device called a single-positron quantum cyclotron, which uses electric and magnetic fields to hold the particle in a vacuum at a temperature close to absolute zero, so it never touches a wall. 1 2 Left · 1Antimatter annihilates on contact with ordinary matter, releasing energy, which is why it has to be isolated in vacuum chambers and electromagnetic fields. 1

Right · 1The New York Post, citing the findings in Physical Review Letters, reports that the team caught the positron as it shot out of radioactive material and cooled it to 0.3 degrees above absolute zero; Gabrielse said the hardest part was slowing the fast particle enough to catch it. 2 Mixed · 2The particle was held in its lowest energy state, which let the researchers induce controlled changes in its quantum behaviour without destroying it, so measurements could be repeated. 1 2 Left · 1The aim is to compare the magnetic properties of positrons and electrons, which have the same mass but opposite charge. Electrons have been measured very precisely, but positrons have been harder to match. 1

Mixed · 2According to the American Physical Society, the new device could make such antimatter measurements about 30 times more precise than before. 1 2 Mixed · 2So far no unexpected difference between positron and electron has been found. Gabrielse said current theories predict none, and that if the two proved unequal, "that would be the biggest discovery in physics in the last century". 2 1 Mixed · 2The work bears on why the universe is made almost entirely of ordinary matter, although theory suggests the Big Bang should have produced equal amounts of both. 1 2