First evidence of antihyperhelium-4 found
The most exotic known atomic nucleus differs from normal antimatter in that it contains a strange building block. It is said to provide information about fundamental properties of the universe.
Increasing evidence suggests that the most exotic atomic nucleus known to date was created at the CERN research institute in 2018. According to a publication submitted to the journal Physical Research Letters, antihyperhelium-4 - a heavier version of antihelium-4 - was formed when lead atomic nuclei collided. As the ALICE experiment team reports, the measurements do not yet reach the statistical significance required for a formal discovery - but the data fits well with the theoretically expected properties of the particle. Experts hope that the exotic antimatter nuclei will provide evidence of subtle differences between matter and antimatter. These should help explain why there is so much more matter than antimatter in the universe.
In addition to protons and neutrons, hyper-atomic nuclei also contain so-called hyperons - nuclear building blocks that consist not only of up and down quarks, but also of their heavier relatives, for example strange quarks. In the atomic nucleus, hyperons behave like normal nuclear building blocks, except that they are much heavier and decay much faster. Hyperons and the hypernuclei made up of them form in the quark-gluon plasma, which is created for fractions of a second when two lead atomic nuclei collide with high energy.
Since there are a total of six types of quark, three of which are interchangeable in principle, a whole zoo of different hyperons can be formed. The nucleus of the newly discovered antihyperhelium-4 contains two antiprotons and an antineutron, while the fourth antineutron is replaced by an anti-Λ-hyperon. It consists of three antiquarks: up, down and strange. The latter does not normally occur in nuclear components and is around 20 times heavier than the analogue down quark.
The antihyperhelium-4 is one of three antimatter hypernuclei discovered so far. Previously, the Brookhaven National Laboratory had already produced the heavy antihydrogen counterparts antihypertritium and antihyperhydrogen-4. Experts hope to find parity violations more easily in such massive nuclei - in other words, that matter and antimatter behave differently. This could help explain one of the strangest properties of the universe. Matter and antimatter were created in equal measure in the Big Bang, but today only matter is found in the universe. However, antihyperhelium-4 did not fulfil this hope: the nucleus behaved in exactly the same way as its counterpart made of normal matter.
Spectrum of Science
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