Particle physics: Going with the antimatter flow

A new source for antihydrogen atoms that allows for in-flight measurements of their properties several metres away from their originating magnetic environment, which normally disrupts their behaviour, is presented in this week’s Nature Communications. The production method should enable spectroscopy experiments to probe the fundamental properties of antimatter.

While theory predicts that matter and antimatter should be entirely equivalent, so far we have been unable to experimentally prove this. Spectroscopic measurements of atomic transitions tell us much about the fundamental properties of matter, and high-precision measurements of the transitions in hydrogen have now been achieved. Yet precise measurements of the equivalent transitions in antihydrogen atoms remain elusive.

Naofumi Kuroda and colleagues working at the Antiproton Decelerator facility at CERN, have now developed a source of antihydrogen atoms that should allow such experiments to be possible. Their source uses carefully controlled magnetic fields to mix positrons (anti-electrons) and antiprotons to form antihydrogen atoms. But unlike other antihydrogen generation sources, their magnetic trap preferentially creates antimatter atoms that continue to flow in a specific direction. These antihydrogen atoms can be injected out of the trap and the team were able to measure their stream up to 2.7 metres away. This controlled flow of antimatter can then be used for future in-flight spectroscopic measurements outside of the magnetic environment of the trap, providing access to the ground state of antihydrogen for direct comparison with its normal matter counterpart.