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Andrei Sakharov's four page letter in the Soviet Journal of Experimental and Theoretical Physics in 1967 is one of the boldest and most famous physics papers of the century. Its aim was to explain why the matter in the universe is built of protons, neutrons, and electrons, while antiprotons, antineutrons, and positrons are so rare that we can observe antimatter only when it is produced in high-energy collisions, mainly in particle accelerators. This particle-antiparticledisparity is usually referred to as the "baryon asymmetry of the universe," protons and neutrons being the lightest of allbaryons. Sakharov made the elegant assumption that originally the universe was neutral and had no baryon asymmetry. He then had the brilliant insight to realize that an asymmetry would build up following the big bang, via nonstationaryprocesses during the expansion of the early universe, if his novel idea of proton instability were combined with the violation of particle-antiparticle symmetry (CP symmetry), which James Cronin, Val Fitch, and their collaborators had discovered experimentally in 1964 in decays of kaons. Many features of Sakharov's specific model of these processes became characteristic of grand unification models proposed in the 1970s, and the discovery of proton decay became, and remains today, the goal of several very-large-scaleunderground detectors.This summer it was discovered that the particle - antiparticle symmetry is also violated in the decay of a second family of particles known as the B-mesons. This most recent observation was reported by an international collaborationincluding more than 600 scientists and engineers from 73 institutions around the world, including Russia, working at the Stanford Linear Accelerator Center, operated by Stanford University on behalf of the U.S. Department of Energy. Itconfirms this phenomenon for the first time definitely in this second family of particles known as the B mesons and adds strength to this approach of Sakharov to understanding the matter asymmetry in the universe. This result has beensubmitted to Physical Review Letters on July 5 for publication later this summer.
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