49_quarks - Lesson 49 Quarks By 1960 physicists felt pretty...

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Lesson 49: Quarks By 1960 physicists felt pretty much like you do right now... confused! Leptons are really small, and there are only six of them (and their antiparticles), so it seems like they are probably fundamental particles. The hadrons ( mesons and baryons ) are really big, and there are so many of them, that it seems like maybe they are made up of just a few other smaller fundamental particles. In 1963 Murray Gell-Mann and George Zweig independently suggested the properties of the fundamental particles that make up the hadrons, named quarks . In their original work they were able to show that all the hadrons known at the time could be made up of just three quarks. To explain the two most important hadrons, protons and neutrons, we only need two of these quarks... up quark with a 2 3 e charge → symbol is u. down quark with a 1 3 e charge → symbol is d. This bothered physicists, since it involved having charges that were a fraction of an elementary charge, which had never been seen. By 1967 the Stanford Linear Accelerator was being used to shoot high energy electrons at protons. The electrons deflected around the proton in an uneven pattern that suggested the charge of a proton was not evenly spread out, just as the quark model suggested.
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