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Concept
Charm quark
Summary
The charm quark, charmed quark, or c quark is an elementary particle of the second generation. It is the third-most massive quark, with a mass of 1.27GeV/c2 (as measured in 2022) and a charge of +2/3 e. It carries charm, a quantum number. Charm quarks are found in various hadrons, such as the J/psi meson and the charmed baryons. There are also several bosons, including the W and Z bosons and the Higgs boson, that can decay into charm quarks.
The charm quark was first predicted in 1964 by James Bjorken and Sheldon Glashow, and predicted again in 1970 by Glashow, John Iliopoulos, and Luciano Maiani. In 1974, it was discovered through the J/psi meson separately at Brookhaven National Laboratory and the Stanford Linear Accelerator Center. In the next few years, several charmed particles including the D meson and the charmed strange mesons were found.
In the 21st century, a baryon containing two charmed quarks has been found. There is recent evidence that intrinsic charm quarks exist in the proton, and the coupling of the charm quark and the Higgs boson has been studied. Recent evidence also indicates CP violation in the decay of the D0 meson, which contains the charm quark.
According to Sheldon Glashow, the charm quark received its name because of the "symmetry it brought to the subnuclear world." Glashow also justified the name as "a magical device to avert evil", for adding the charm quark would prohibit unwanted and unseen decays in the three-quark theory at the time.
The charm quark is also called the "charmed quark" in both academic and non-academic contexts. The symbol of the charm quark is "c".
Quark model
In 1961, Murray Gell-Mann introduced the Eightfold Way as a pattern to group baryons and mesons. In 1964, Gell-Mann and George Zweig independently proposed that all hadrons are composed of elementary constituents, which Gell-Mann called "quarks". Initially, only three quarks were proposed: the up quark, the down quark, and the strange quark. These quarks would produce all the particles in the Eightfold Way.
Official source
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