quark

In physics, the elementary particle that is the fundamental constituent of all hadrons (subatomic particles that experience the strong nuclear force and divided into baryons, such as neutrons and protons, and mesons). Quarks have electric charges that are fractions of the electronic charge (+2/3 or −1/3 of the electronic charge). There are six types, or ‘flavours’: up, down, top, bottom, strange, and charmed, each of which has three varieties, or ‘colours’: red, green, and blue (visual colour is not meant, although the analogy is useful in many ways). To each quark there is an antiparticle, called an antiquark. See quantum chromodynamics (QCD).

The existence of the top quark was confirmed by two teams of physicists at Fermilab in March 1995. It is unstable, lasting about 10−25 second (a ten-millionth of a billionth of a billionth of a second). It is almost as massive as a gold atom.