down quark

[Julian]

a stable quark with an electric charge of -1/3 and a mass 607 times that of an electron

[KalanNug]

A quark having a fractional electric charge of -1/3 and a mass about 4 to 8 MeV. Symbol: d

[Dave Paprocki]

A down quark is a type of elementary particle and a fundamental constituent of matter. It is the second-lightest of all quarks, a type of particle that makes up protons and neutrons. Down quarks carry an electric charge of -1/3 e. The existence of down quarks, along with up quarks and electrons, is sufficient to reproduce the entire chemistry of the universe, as they are the components needed to form neutrons, protons and electrons. They interact via all four fundamental forces of physics: gravitation, electromagnetism, weak interactions, and strong interactions.

[Thu Thi Le]

The down quark or d quark is the second-lightest of all quarks, a type of elementary particle, and a major constituent of matter. Together with the up quark, it forms the neutrons and protons of atomic nuclei. It is part of the first generation of matter, has an electric charge of −¹⁄3 e and a bare mass of 4.1–5.7 MeV/c². Like all quarks, the down quark is an elementary fermion with spin-¹⁄2, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions. The antiparticle of the down quark is the down antiquark, which differs from it only in that some of its properties have equal magnitude but opposite sign.
Its existence was postulated in 1964 by Murray Gell-Mann and George Zweig to explain the Eightfold Way classification scheme of hadrons. The down quark was first observed by experiments at the Stanford Linear Accelerator Center in 1968.