Antimatter of Fact: Collider Generates Most Massive Antinucleus Yet

 

SHADOW DANCE: Within the shower of particles produced in collisions of gold ions, researchers have identified rare and fleeting antimatter helium 4 nuclei. Image: STAR Collaboration/BNL

 

Most people know two things about helium. One is that it makes your voice comically high-pitched when you inhale it; the other is that it is extremely light, which is why balloons filled with the stuff float upward through the heavier air. But in particle physics terms—and especially when it comes to the nuclear physics of antimatter—helium is no lightweight. With two protons and two neutrons, ordinary helium is four times as massive as hydrogen, the lightest element. (Both hydrogen and helium have other stable isotopes—atomic varieties with differing masses—but they are rare in nature.)

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