Scientists at the Large Hadron Collider (LHC) have made an exciting discovery—the antimatter version of hyperhelium-4.
This achievement, reported by the ALICE collaboration, marks the first-ever evidence of this exotic particle, pushing the boundaries of our understanding of antimatter and the early universe.
Hyperhelium-4 is a rare type of hypernucleus, which is an atomic nucleus made up of protons, neutrons, and hyperons.
Hyperons are unstable particles containing a strange quark. Antihyperhelium-4, the antimatter counterpart, consists of two antiprotons, one antineutron, and an antilambda (an anti-hyperon).
This discovery builds on a previous finding earlier this year by the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC), where antihyperhydrogen-4 was detected.
The new discovery of antihyperhelium-4 is significant not only because it is the heaviest antimatter hypernucleus ever observed at the LHC but also because it provides more clues about the universe’s matter-antimatter imbalance.
The ALICE team studied data from lead–lead collisions at an energy of 5.02 teraelectronvolts (TeV) per nucleon pair, collected in 2018.
These high-energy collisions create quark-gluon plasma, a state of matter thought to have existed just a millionth of a second after the Big Bang. They also produce exotic particles like hypernuclei and their antimatter counterparts.
Using advanced machine-learning techniques, the researchers searched for evidence of hyperhydrogen-4, hyperhelium-4, and their antimatter forms. The decay patterns of these particles were key to identifying them. For instance, antihyperhelium-4 decays into an antihelium-3 nucleus, an antiproton, and a charged pion.
The team found evidence of antihyperhelium-4 with a statistical significance of 3.5 standard deviations, meaning the chances of this result being random are extremely low. They also found antihyperhydrogen-4 with a significance of 4.5 standard deviations.
The study measured the production rates and masses of these hypernuclei, finding that they match existing predictions. The results also align with the statistical hadronization model, which describes how particles form in high-energy collisions.
Interestingly, the study revealed equal production rates for antimatter and matter versions of these hypernuclei, consistent with previous LHC findings. This balance provides insights into the conditions of the early universe and the mysterious asymmetry that led to the dominance of matter over antimatter today.
This discovery not only sheds light on the production of rare antimatter particles but also strengthens our understanding of the forces at play in the universe’s infancy.
As physicists continue to explore these exotic particles, we may uncover even more secrets about the origins and structure of our universe.
