Our collection of antimatter has just gotten heavier, as researchers have logged the heaviest antimatter version of an atomic nucleus yet, called antihyperhydrogen-4.
“We didn’t think that it was 100 per cent certain we would find it, we just knew we had a chance,” says at the Institute of Modern Physics in China. He and his colleagues, an international team called the STAR Collaboration, briefly formed the new type of antimatter in an experiment at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC) in New York.
RHIC can accelerate heavy nuclei of atoms like gold to up to 99.996 per cent of the speed of light, then smash them together to create an extremely hot particle soup, which enables unusual combinations of matter and antimatter. Among about 6 billion collisions in the new experiment, the mix of particles and antiparticles was just right for antihyperhydrogen-4 to form 16 times. In each case, it only stayed stable for about 100 trillionths of a second.
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This particular form of antimatter consists of an antiproton and two antineutrons – antimatter versions of the protons and neutrons found in a standard atom’s nucleus – plus one especially exotic antimatter particle called an antihyperon. It is the antimatter counterpart of the hyperon, a particle that contains at least one rare and heavy “strange quark”. Thanks to these components, the new particle is considered a very exotic antimatter “hypernucleus” – and is the heaviest one made so far.
“The fact that you can pick out these extremely rare events and see antimatter things that, in principle, must exist but are very, very hard to make in a world dominated by matter, that’s impressive to me,” says at the University of Maryland. “It’s basically anti-alchemy.”
Beyond confirming that antihyperhydrogen-4 exists and can be made, the new experiment is part of a long effort to understand the differences between matter and antimatter, says Qiu. Our best theories of the universe suggest that, in its earliest stages, it was filled with equal amounts of matter and antimatter, which should have annihilated into nothingness. Why this didn’t happen remains an open question – and studying each new antimatter particle may bring us closer to the answer, says Qiu.
Nature
