Down quark

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Down quark

The down quark (symbol d) is one of the basic building blocks of matter. It is a fermion with electric charge -1/3, spin 1/2, and it carries color charge. It is part of the first generation of matter and combines with up quarks to form protons and neutrons: proton = two up quarks and one down quark (uud); neutron = one up quark and two down quarks (udd). Because protons and neutrons make up atomic nuclei, down quarks are found in all everyday matter.

The bare mass of a down quark is about 4.7 MeV/c^2, but quarks inside particles have larger effective masses due to binding energy. For example, a down quark inside a proton behaves as if it has a mass of a few hundred MeV/c^2. The down quark has an antiparticle, the down antiquark.

The down quark was proposed in 1964 by Murray Gell-Mann and George Zweig to help explain the pattern of hadrons, and it was first observed in experiments at the Stanford Linear Accelerator Center in 1968.

In weak interactions, a down quark can transform into an up quark, emitting an electron and an electron antineutrino. Overall, the down quark is a fundamental component of matter and a key part of the particles that make up atomic nuclei.