Measurement of the hyperfine structure of antiprotonic helium

This paper discusses the level splitting of the antiprotonic helium atomcul e, an exotic atom consisting of a helium nucleus, an electron, and an antip roton which occupies highly excited states with angular momentum of L appro ximate to 30-35. The observation of a splitting in a laser transition betwe en two levels is presented, and an experiment in preparation at the forthco ming AD facility at CERN is described which aims at directly measuring the level splitting by using a 2-laser microwave triple resonance technique. Th is experiment has the potential to determine the magnetic moment of the ant iproton with higher precision than currently known.