The nature of the ${\bar p}$ metastability in helium

Abstract

A new interpretation of the nature of the metastable states of antiprotons in helium is proposed. The first step is the formation of an ion ($\bar p\alpha ee$), which shall be called “ioncule”. After its decay a neutral “atomcule” ($\bar p\alpha ee$) is formed which was observed in the experiments on metastable antiprotonic helium. This model explains the experiments in a natural way, in particular the quenching by atomic and molecular admixtures and the pressure dependence of quenching in pure helium. At high helium densities the ioncule creates a vacuum bubble in helium. It is shown that the annihilation of slowed-down ${\bar p}$ can be suppressed at helium pressures of ∼ 10 000 bar.