The up quark is a first-generation quark with a charge of +(2/3)e. It is the lightest of all quarks, with a bare mass of between 1.5 and 4 MeV. According to the Standard Model of particle physics, it and the down quark are the fundamental constituents of the nucleons; the proton contains two up quarks and a down quark, while the neutron contains one up quark and two down quarks. (Note that the majority of the mass in nucleons comes from the energy in the gluon field holding the quarks together, and not the quark masses themselves.)

The existence of up quarks was first postulated when Gell-Mann and Zweig developed the quark model in 1964, and the first evidence for them was found in deep inelastic scattering experiments at SLAC in 1967.

Hadrons containing up quarks

Some of the hadrons containing up quarks include:

• Charged Pions (π^±) are mesons containing an up quark and an anti-down quark, or vice versa.
• The neutral pion (π⁰) is a linear combination of up-antiup and down-antidown, as are the ρ and ω mesons.
• The η and η' flavorless mesons are linear combinations of several quark-antiquark pairs, including up-antiup.
• A large number of detected baryons contain one or more up quarks. Like the nucleons, the Δ baryons are made of only up and down quarks: the Δ⁺⁺ contains three up quarks, the Δ⁺ contains two, and the Δ⁰ contains only one.

See also

• Isospin

Quarks

Quark arriba | 위 쿼크 | Quark up | Kwark górny | Quark u | 上夸克