Dec 10, 2024 21:00:00

CERN discovers antihyperhelium-4, the heaviest antihypernucleus created in an experiment at the Large Hadron Collider

On December 9, 2024,

the European Organization for Nuclear Research (CERN) reported that it had discovered a new hypernucleus , 'antihyperhelium-4,' in an experiment using the Large Hadron Collider (LHC) to recreate the high-energy conditions at the birth of the universe.

Antihyperhelium-4: First Evidence at the LHC - CERN Document Server
https://cds.cern.ch/record/2917859

ALICE finds first ever evidence of the antimatter partner of hyperhelium-4 | CERN
https://home.cern/news/news/physics/alice-finds-first-ever-evidence-antimatter-partner-hyperhelium-4

While normal atomic nuclei are composed of neutrons and protons , hypernuclei are composed of not only protons and neutrons but also particles called hyperons ( baryons ). Hyperons are baryons that contain strange quarks , a type of elementary particle.

Hypernuclei are important for understanding how atomic nuclei are formed, but hyperons are unstable and have a lifespan of only about one billionth of a second, much shorter than nucleons made up of atoms and neutrons. They are also extremely difficult to create in the laboratory, making them a fascinating research subject for physicists.

The ALICE experiment, which uses the Large Hadron Collider at CERN, will accelerate and collide heavy ions to produce quark-gluon plasma, the hot, high-pressure state of matter that is believed to have filled the universe a millionth of a second after the Big Bang. It will also create the conditions suitable for the production of atomic nuclei and hypernuclei, as well as their antimatter counterparts , antinuclei and antihypernuclei.

The ALICE experiment will produce a large number of hypernuclei, but so far only the lightest hypernucleus , hypertriton , its antimatter equivalent , antihypertriton , and antihyperhydrogen-4, which was discovered in 2024, have been observed at the LHC .

A new CERN research team used data from lead-lead collision experiments conducted in 2018 to search for traces of hypernuclei and antihypernuclei using machine learning techniques that are superior to conventional hypernuclear search techniques.

As a result of the analysis, we found evidence for the existence of antihyperhelium-4 with a significance of 3.5

standard deviations . Antihyperhelium-4 is an antihypernucleus consisting of two antiprotons, one antineutron and one antilambda particle , and is also the heaviest antihypernucleus found to date at the LHC.

The Big Bang should have produced equal amounts of matter and antimatter, but there is an imbalance in the current universe where matter dominates. Measuring hypernuclei and antihypernuclei will help investigate this imbalance in the current universe.