Metastable antiprotonic helium atoms: Past, present and future

Abstract

This review briefly summarises the experimental studies carried out on metastable antiprotonic helium over the last few years, and points out a possible way ahead, assuming that very low-energy antiprotons continue to be available. Very recently, an abundance of new results has been found by the Japanese-European collaboration working in these exotic atoms at LEAR, the Low Energy Antiproton Ring at CERN. Together with tremendous progress in several of the techniques needed for antihydrogen synthesis, this has provided new hope that some way will be found to continue this fruitful line of research after the closure of this excellent machine.