UpQuark

The up quark is a fundamental constituent of matter and one of the six flavors of quarks in the Standard Model. It is a first-generation quark with electric charge +2/3 of the elementary charge, carries color charge, has spin 1/2, and a baryon number of +1. Quarks interact via the strong force, exchanging gluons, and also participate in electromagnetic and weak interactions.

In the current (bare) quark-mass scheme, the up quark has a mass of roughly 2 to 3 MeV/c^2; inside hadrons its effective, or constituent, mass is typically several hundred MeV/c^2 due to strong interactions. Up quarks combine with down quarks to form nucleons: the proton consists of two up quarks and one down quark (uud), and the neutron consists of one up quark and two down quarks (udd). Mesons may contain up quarks as well, for example the charged pion π+ consists of an up quark and an anti-down quark (u d̄).

The up quark participates in all three fundamental interactions of the Standard Model. It changes flavor through charged weak currents, described by the CKM matrix, and its dynamics are governed by quantum chromodynamics for the strong interaction. Quarks are confined and cannot be observed in isolation. Historically, the up quark, along with the down quark, was proposed in 1964 by Murray Gell-Mann and George Zweig as part of the quark model, with supporting evidence from deep inelastic scattering experiments at SLAC in 1968.