ScienceDaily (Apr. 25, 2011) — Eighteen examples of the heaviest antiparticle ever found, the nucleus of antihelium-4, have been made in the STAR experiment at RHIC, the Relativistic Heavy Ion Collider at the U.S. Department of Energy's Brookhaven National Laboratory.
"The STAR experiment is uniquely capable of finding antihelium-4," says the STAR experiment's spokesperson, Nu Xu, of the Nuclear Science Division (NSD) at Lawrence Berkeley National Laboratory (Berkeley Lab). "STAR already holds the record for massive antiparticles, last year having identified the anti-hypertriton, which contains three constituent antiparticles. With four antinucleons, antihelium-4 is produced at a rate a thousand times lower yet. To identify the 18 examples required sifting through the debris of a billion gold-gold collisions."
Collisions of energetic gold nuclei inside STAR briefly recreate conditions in the hot, dense early universe only millionths of a second after the big bang. Since equal amounts of matter and antimatter were created in the big bang they should have completely annihilated one another, but for reasons still not understood, only ordinary matter seems to have survived. Today this excess matter forms all of the visible universe we know.