EXTREME RARITY. “Very recently, tantalizing hints of anti-3He and anti-4He candidates have been presented by the AMS-02 magnetic spectrometer. Considering the huge helium statistics, about one antihelium candidate out of 100 million helium events, a daunting simulation effort is required to exclude misidentification of these events.”
https://link.springer.com/content/pdf/10.1007/s10686-021-09708-w.pdf