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Quarks have fractional electric charge values – either (− 1 / 3 ) or (+ 2 / 3 ) times the elementary charge (e), depending on flavor. Up, charm, and top quarks (collectively referred to as up-type quarks) have a charge of + 2 / 3 e; down, strange, and bottom quarks (down-type quarks) have a charge of − 1 / 3 e.
Low-energy electrons do scatter in this way, but, above a particular energy, the protons deflect some electrons through large angles. The recoiling electron has much less energy and a jet of particles is emitted. This inelastic scattering suggests that the charge in the proton is not uniform but split among smaller charged particles: quarks.
Electrons surround a nucleus made of protons and neutrons, which contain up and down quarks. The second and third generations of charged particles do not occur in normal matter and are only seen in extremely high-energy environments such as cosmic rays or particle accelerators .
Quarks are massive spin-1 ⁄ 2 fermions that carry a color charge whose gauging is the content of QCD. Quarks are represented by Dirac fields in the fundamental representation 3 of the gauge group SU(3). They also carry electric charge (either − 1 ⁄ 3 or + 2 ⁄ 3) and participate in weak interactions as part of weak isospin doublets.
Two terms are used in referring to the mass of the quarks that make up protons: current quark mass refers to the mass of a quark by itself, while constituent quark mass refers to the current quark mass plus the mass of the gluon particle field surrounding the quark. [45]: 285–286 [46]: 150–151 These masses typically have very different values
Composite bosons (especially 2 quarks), in which case they are called mesons. Quark models, first proposed in 1964 independently by Murray Gell-Mann and George Zweig (who called quarks "aces"), describe the known hadrons as composed of valence quarks and/or antiquarks, tightly bound by the color force, which is mediated by gluons.
It is possible to create all fundamental particles in the standard model, including quarks, leptons and bosons using photons of varying energies above some minimum threshold, whether directly (by pair production), or by decay of the intermediate particle (such as a W − boson decaying to form an electron and an electron-antineutrino).
The up quark or u quark (symbol: u) is the lightest of all quarks, a type of elementary particle, and a significant constituent of matter.It, along with the down quark, forms the neutrons (one up quark, two down quarks) and protons (two up quarks, one down quark) of atomic nuclei.