The quark model was originally just a very good classification scheme to organize the depressingly large number of hadrons that were being discovered starting in the 1950s and continuing through the 1960s but it received experimental verification beginning in the late 1960s and continuing to the present. Hadrons are not "fundamental", but their "valence quarks" are thought to be, the quarks and antiquarks which give rise to the quantum numbers of the hadrons.
These quantum numbers are labels identifying the hadrons, and are of two kinds. One set comes from the Poincaré symmetry—JPC, where J, P and C stand for the total angular momentum, P-symmetry, and C-symmetry respectively. The remainder are flavour quantum numbers such as the isospin, strangeness, charm, and so on. The quark model is the follow-up to the Eightfold Way classification scheme.
All quarks are assigned a baryon number of 1⁄3. Up, charm and top quarks have an electric charge of +2⁄3, while the down, strange, and bottom quarks have an electric charge of −1⁄3. Antiquarks have the opposite quantum numbers. Quarks are also spin-1⁄2 particles, meaning they are fermions.
Mesons are made of a valence quark−antiquark pair (thus have a baryon number of 0), while baryons are made of three quarks (thus have a baryon number of 1). This article discusses the quark model for the up, down, and strange flavours of quark (which form an approximate SU(3) symmetry). There are generalizations to larger number of flavours.
Other articles related to "quark model, model, quark, quarks":
... While the quark model is derivable from the theory of quantum chromodynamics, the structure of hadrons is more complicated than this model reveals ... The full quantum mechanical wave function of any hadron must include virtual quark pairs as well as virtual gluons ... Also, there may be hadrons which lie outside the quark model ...
... In the eventual Standard Model of particle physics codified in the 1970s, all mesons other than the mu meson were finally understood to be hadrons—that ... In the quark model, a meson was no longer defined by mass (for some had been discovered that were very massive—more than the lightest nucleons), but instead ... themselves to be fundamental particles (leptons) like electrons, with no quark structure ...
... The quark model was independently proposed by physicists Murray Gell-Mann and George Zweig in 1964 ... At the time of the quark theory's inception, the "particle zoo" included, amongst other particles, a multitude of hadrons ... but were instead composed of combinations of quarks and antiquarks ...
... Non-quark model mesons include exotic mesons, which have quantum numbers not possible for mesons in the quark model glueballs or gluonium, which have no valence quarks at all tetraquarks ... Typically, every quark model meson comes in SU(3) flavor nonet an octet and a flavor singlet ... is agreement that one of several states is one of these non-quark model mesons, the degree of mixing, and the precise assignment is fraught with uncertainties ...
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