Particle physics: Record-breaking heavy atomic nucleus made of antimatter discovered
In the search for the reason for the imbalance between matter and antimatter, researchers keep coming across exotic particles. Now they have found antihyperhydrogen-4.
An international research group has discovered the heaviest atomic nucleus of antimatter observed to date - so-called antihydrogen-4, an exotic variant of antihydrogen. As the collaboration reports in the scientific journal "Nature", it is an atomic nucleus consisting of an antiproton, two antineutrons - the respective antiparticles of the proton and the neutron - and an antilambda particle, a combination of an anti-up, anti-down and anti-strange quark. They used the STAR detector at the Relativistic Heavy Ion Collider (RHIC), a particle accelerator on the grounds of Brookhaven National Laboratory in the USA. The researchers found a total of 16 atomic nuclei of antihyperhydrogen-4 in the data.
According to the theory, every elementary particle has an antiparticle. Both have the same properties, for example exactly the same mass. However, their charges are opposite. Opposites attract, they say. In the case of matter and antimatter, they even annihilate each other. They are said to disintegrate in an annihilation reaction. This creates other, lighter particles. However, even after decades of intensive research, antimatter continues to pose numerous mysteries. For example, there is still no convincing explanation as to why matter and antimatter must have been created in equal parts during the Big Bang, but why the universe we see today consists only of matter.
In order to find the reason for this tiny imbalance, researchers around the world are trying to simulate the conditions that prevailed shortly after the Big Bang - such as extreme temperatures and pressures. To do this, they accelerate protons, electrons or even larger atomic nuclei to almost the speed of light in huge facilities and let them collide. The decay products can be used to investigate how matter and antimatter are structured and how they interact.
No evidence of deviations from theory
The RHIC accelerator is normally used to research the quark-gluon plasma and the spin structure of the proton. In 2011, the heaviest antimatter element to date, antihelium-4, was created and observed there. The researchers have now analysed the data from six billion collisions of gold nuclei and made a remarkable discovery: a previously undiscovered, exotic atomic nucleus made of antimatter - antihyperhydrogen-4. For such an atomic nucleus to form, an antiproton, two antineutrons and an antilambda particle must collide in one place. This happens extremely rarely. An antilambda particle is a very short-lived particle that consists of an anti-up quark, an anti-down quark and an anti-strange quark.
Since antihydrogen-4 is also very short-lived and decays again within fractions of a second, the scientists had to take a diversion via the known decay products: Antihelium-4 and a pion, the latter consisting of a quark and an anti-quark. Using these more stable particles, they were then able to conclude that the exotic, heavy anti-atomic nucleus must have existed for a brief moment.
In a next step, the researchers compared the lifetime of antihydrogen-4 with that of hyperhydrogen-4, i.e. the counterpart made of normal matter. They found no difference. Although this confirms current physical models, it again provides no clue as to how the imbalance of matter and antimatter in the universe comes about.
Spectrum of Science
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