Single Positron Trapped for Months in Antimatter Test — SkimNews
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- Gerald Gabrielse and colleagues at Northwestern University trapped a single positron for months using electromagnetic fields, after slowing antiparticles emitted by a radioactive sodium isotope through a tungsten crystal and refrigerating them to near absolute zero.
- Stefan Ulmer of Japanese scientific institute RIKEN called the trapping "extremely difficult," requiring the chamber to be emptied of all other particles and held just tenths of a degree above the coldest temperature possible, any stray particle or vibration risks disturbing the antiparticle.
- The team cooled the positron into its lowest energy state and observed controlled "quantum jumps" to the next-lowest state using microwave bursts, demonstrating precise quantum control of an isolated antiparticle.
- Researchers plan to measure the positron's magnetic moment — its response to magnetic fields — and compare it with the most precise measurement ever made of the electron's magnetic moment to test whether matter and antimatter truly mirror each other.
- The standard model predicts identical magnetic moments for the electron and positron, a prediction Gabrielse called "inconsistent, or at least significantly incomplete" because it cannot explain why the universe contains matter rather than nothing.
- Ulmer said the work "has the potential to become one of the most precise measurements of a fundamental constant in physics," with Gabrielse aiming to have comparative data within the year.
- The result was published in Physical Review Letters, with the team positioning any divergence between electron and positron magnetic moments as a possible window into why matter dominates the cosmos.
Why it matters: If the positron's magnetic moment deviates even slightly from the electron's, physicists would have the first concrete empirical crack in the standard model's explanation of matter-antimatter symmetry — potentially explaining why the universe exists at all rather than having annihilated itself at the Big Bang. With data expected within the year, the measurement would give theorists a real number to build new physics around.
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