According to current physics, equal amounts of matter and antimatter existed at the beginning of the universe, and their properties are symmetrical. However, some mysterious physical mechanism caused the annihilation of most matter and antimatter, causing about one out of ten billion particles to survive.
What caused the difference in quantities of matter and antimatter in the universe?
Creating new antimatter in the laboratory and studying its properties is essential to find the answer.
Antimatter is extremely rare. It quickly annihilates with surrounding matter. What’s more difficult is producing antimatter nuclei and antimatter hypernuclei (nuclei containing hyperons such as Lambda) by combining several antibaryons.
Since 1928, scientists have discovered only six antimatter (hyper)nuclei types.
Now, physicists from the STAR Collaboration have observed a new antimatter hypernucleus, antihyperhydrogen-4, for the first time. This is the heaviest antimatter hypernucleus discovered in experiments to date.
This new antimatter hypernucleus antihyperhydrogen-4 consists of one antiproton, two antineutrons, and one anti-Lambda hyperon. The anti-Lambda hyperon in it is unstable, so the antihyperhydrogen-4 decays after traveling merely a few centimeters.
This discovery was made at the Relativistic Heavy Ion Collider (RHIC) in the United States.
WU Junlin, a PhD student at IMP, said, “After analyzing experimental data of approximately 6.6 billion heavy-ion collision events, we reconstructed antihyperhydrogen-4 from its decay products antihelium-4 and π+ meson, and identified a signal of about 16 antihyperhydrogen-4.”
When scientists measured its lifetime, they found no significant difference between its corresponding particle hyperhydrogen-4 within the limits of measurement precision. This verifies the symmetry between matter and antimatter properties.
This discovery is a significant advancement in the exploration of antimatter and the understanding of matter-antimatter symmetry.
Journal Reference:
- STAR Collaboration. Observation of the antimatter hypernucleus. Nature (2024). DOI: 10.1038/s41586-024-07823-0