Scientists studying the tracks of particles streaming from six billion collisions of atomic nuclei at the Relativistic Heavy Ion Collider (RHIC)—an "atom smasher" that recreates the conditions of the early universe—have discovered a new kind of antimatter nucleus, the heaviest ever detected. Composed of four antimatter particles—an antiproton, two antineutrons, and one antihyperon—these exotic antinuclei are known as antihyperhydrogen-4.
