An unprecedented measurement of an antiproton suggests that matter and antimatter truly mirror each other.

Gerald Gabrielse at Harvard University in Cambridge, Massachusetts, and his group began with a particle trap designed to measure the proton's magnetic moment — the amount of force that its magnetic spin can exert. They shipped the equipment to the world's largest particle-physics laboratory — CERN near Geneva, Switzerland — where they confined a single antiproton from the CERN beam and measured the strength of its magnetic moment. The moment of the antiproton differed from that of the proton by less than 5 parts per million, the most precise measurement ever achieved. This result is in agreement with established theory of symmetry between particles and their antimatter counterparts.

Phys. Rev. Lett. 110, 130801 (2013)