A single positron is trapped for months and cooled to its lowest energy state

A Northwestern University team built a one-positron quantum cyclotron that slows positrons from radioactive decay, selects survivors and holds one particle in an electromagnetic trap for months before cooling it to its lowest energy state. The goal is to measure the positron's magnetic moment and compare it with the electron's. That property can be measured about 10,000 times more precisely for electrons and positrons than for protons and antiprotons, so a repeatable mismatch could point beyond the standard model and help explain why the Universe is overwhelmingly matter. The work published on October 21 establishes the platform; it does not yet report matter-antimatter asymmetry. Source efficiency, particle loss, systematic error and independent replication remain central to the precision test ahead.