Measurement of the hyperfine structure of antiprotonic helium

This paper discusses the level splitting of the antiprotonic helium atomcule, an exotic atom consisting of a helium nucleus, an electron, and an antiproton which occupies highly excited states with angular momentum of L $9 approximately=30-35. The observation of a splitting in a laser transition between two levels is presented, and an experiment in preparation at the forthcoming AD facility at CERN is described which aims at directly measuring the $9 level splitting by using a 2- laser microwave triple resonance technique. This experiment has the potential to determine the magnetic moment of the antiproton with higher precision than currently known. (12 refs).