Quark

Quarks are among the most fundamental particles known, smaller and simpler than the protons and neutrons they build. There are six types, called flavors: up, down, charm, strange, top, and bottom, and they combine in specific groups to form larger particles called hadrons.

A proton is made of two up quarks and one down quark, while a neutron is made of two down quarks and one up quark. Quarks are never found alone in nature, they are always bound together by the strong force, a phenomenon called confinement.

Quarks were proposed independently by Murray Gell-Mann and George Zweig in 1964 to explain patterns in the growing zoo of particles being discovered at the time. Their existence was later confirmed directly in high energy scattering experiments.