Physicists at the Relativistic Heavy Ion Collider (RHIC) on Long Island, New York, say they have made the heaviest antimatter nucleus yet: antihelium-4.
Antimatter particles carry the same mass as normal matter, but the opposite charge. When matter and antimatter collide, they annihilate in a flash of energy. Because we live in a world dominated by regular matter, antiprotons and antineutrons usually annihilate before they can form into antinuclei.
In a paper posted to Arxiv, however, the team announce the creation of 18 nuclei of antihelium-4, which consists of two antiprotons and two antineutrons.
At a vanishingly tiny 6.6 x10-27 kilograms (3.73 gigaelectronvolts/c2), these nuclei nevertheless are more massive than a three-particle isotope of antihydrogen (5.3×10-27 kilograms) that the same team reported in Science last year.
The RHIC smashes gold nuclei together at 200 gigaelectronvolts, dissolving them into a soup of quarks and antiquarks. With luck, enough of these combine to give antimatter nuclei. They don’t hang around long: the half-life of the antihydrogen was a few hundred trillionths of a second.
Antilithium-6 would be the next step but the researchers calculate that yields of this nucleus would be a million times lower than that of antihelium-4, ‘beyond the reach of current accelerator technology’.
More details on the ArXiv blog, and at New Scientist.