![]() ![]() The rules for the oscillations and decays are given by a theoretical framework called the Cabibbo-Kobayashi-Maskawa (CKM) mechanism. This decay happens slightly differently for mesons compared with anti-mesons, which combined with the oscillation means that the rate of the decay varies over time. Since they are unstable, they will “decay” – fall apart – into other more stable particles at some point during their oscillation. They can spontaneously turn into their antiparticle partner and then back again, a phenomenon that was observed for the first time in the 1960. Particles consisting of a quark and an anti-quark are called mesons, and there are four neutral mesons (B 0 S, B 0, D 0 and K 0) that exhibit a fascinating behaviour. The up and down quarks are what make up the protons and neutrons in the nuclei of ordinary matter, and the other quarks can be produced by high-energy processes – for instance by colliding particles in accelerators such as the Large Hadron Collider at CERN. Quarks come in many different kinds, or “flavours”, known as up, down, charm, strange, bottom and top plus six corresponding anti-quarks. The behaviour of quarks, which are the fundamental building blocks of matter along with leptons, can shed light on the difference between matter and antimatter. And it is this surplus that makes up everything we see in the universe today.Įxactly what processes caused the surplus is unclear, and physicists have been on the lookout for decades. This created a small surplus of matter, and as the universe cooled, all the antimatter was destroyed, or annihilated, by an equal amount of matter, leaving a tiny surplus of matter. Scientists believe that in the very hot and dense state shortly after the Big Bang, there must have been processes that gave preference to matter over antimatter. Over the next few decades physicists found that all matter particles have antimatter partners. But in 1932 Carl Anderson discovered an antimatter partner to the electron – the positron – while studying cosmic rays that rain down on Earth from space. At first, it was not clear if this was just a mathematical quirk or a description of a real particle. The existence of antimatter was predicted by physicist Paul Dirac’s equation describing the motion of electrons in 1928. So what happened to it? Using the LHCb experiment at CERN to study the difference between matter and antimatter, we have discovered a new way that this difference can appear. ![]() But today, there’s nearly no antimatter left in the universe – it appears only in some radioactive decays and in a small fraction of cosmic rays. The problem is that would have made it all annihilate. If antimatter and matter are truly identical but mirrored copies of each other, they should have been produced in equal amounts in the Big Bang. ![]() When an antimatter and a matter particle meet, they annihilate in a flash of energy. All the particles that make up the matter around us, such electrons and protons, have antimatter versions which are nearly identical, but with mirrored properties such as the opposite electric charge. It’s one of the greatest puzzles in physics. ![]()
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