User:UnbiasedBrigade/sandbox

Draft for possible "antihelium" article (extremely unfinished; it's only a really small start for now):

Antihelium (helium or 3helium) is the antimatter counterpart of helium. While helium is composed of two protons, two electrons, and a variable number of neutrons, an atom of antihelium is composed of two antiprotons, a variable number of antineutrons, and two positrons. It is theoretically stable, but in practice annihilates with matter very quickly after formation, and thus must be studied quickly after being generated, usually at particle accelerator facilities such as the Relativistic Heavy Ion Collider. As of 2022, only the nuclei have been observed, but they are assumed to form antiatoms by capturing positrons in the same way that matter nuclei do.

Discovery
Antihelium-3 nuclei (3helium) were first observed in the 1970s in proton–nucleus collision experiments at the Institute for High Energy Physics by Y. Prockoshkin's group (Protvino near Moscow, USSR) and later created in nucleus–nucleus collision experiments. Nucleus–nucleus collisions produce antinuclei through the coalescence of antiprotons and antineutrons created in these reactions. In 2011, the STAR detector reported the observation of artificially created antihelium-4 nuclei (anti-alpha particles) (4helium) from such collisions.

The Alpha Magnetic Spectrometer on the International Space Station has, as of 2021, recorded eight events that seem to indicate the detection of antihelium-3.