CP violation: Violation of the CP symmetry of the laws of physics that contributes to explaining the dominance of matter over antimatter in the universe.
For each ►elementary particle there is a corresponding antiparticle. Matter consisting of such antiparticles is called antimatter — and indeed, it has been shown that we can use a particle accelerator to produce antihydrogen atoms. However, such atoms have a short life. For whenever they come into contact with regular matter, both are transformed into pure energy.
Now there is a ►law of nature, the so-called CP symmetry law, according to which antimatter has exactly the same properties as normal matter, except that the antimatter's properties are mirror-images of the corresponding matter's properties and have the opposite electrical charges. For example, in contrast to electrons with their negative charge, positrons — the corresponding antiparticles — are positively charged and rotate in the opposite direction. But there is yet another characteristic difference between matter and antimatter: It appears that our universe consists exclusively of normal matter. Antimatter does not, in actuality, naturally occur in it. And a good thing, too; we would all explode like a hydrogen bomb if we touched a piece of antimatter.
But where does this dominance of matter come from? It must have already come into being shortly after the ►big bang. As early as in 1964, scientists noticed an irregularity in the decay of elementary particles, the so-called mesons.* The decay probabilities of normal mesons turned out to differ from those of antimesons. The difference, however, amounts to no more than 0.2% — not enough to explain the dominance of matter in the universe.
Thus, even within the ►standard model of physics we have a still-unknown law of nature that contibuted to the dominance of matter in the early phase of the universe. It also remains unclear what mechanism causes the violation of CP symmetry. According to one theory, the CP violation is caused by the heavier kinds of ►quarks. To verify this theory we would have to analyze the decay product of particles consisting of one or more of these heavy quark types, such as the bottom quark. Such decays, however, are extremely rare and require enormous experimental effort. At present, scientists are investigating this matter at the great particle accelerator in Stanford, California (SLAC) as well as at the Japanese Nuclear Research Center in Tsukuba. More detailed knowledge of the CP violation could substantially contribute to our understanding of the processes involved in the big bang.
* Mesons consist of two quarks, while nuclear particles such as protons and neutrons each consist of three quarks. There are no isolated quarks in nature.