Antiprotonic helium

Antiprotonic helium is a three-body atom composed of an antiproton and an electron orbiting around a helium nucleus. It is thus made partly of matter, and partly of antimatter. The atom is electrically neutral, since an electron and an antiproton each have a charge of −1 e, whereas a helium nucleus has a charge of +2 e. It has the longest lifetime of any experimentally produced matter–antimatter bound state.^[1]

^ "PROGRESS REPORT OF THE ASACUSA AD-3 COLLABORATION" (PDF). Archived (PDF) from the original on 7 July 2022. Retrieved 30 July 2022.

[1] "PROGRESS REPORT OF THE ASACUSA AD-3 COLLABORATION" (PDF). Archived (PDF) from the original on 7 July 2022. Retrieved 30 July 2022.

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