What Is a Hadron?

Hadrons are composite particles built from quarks bound by gluons. They come in two families: baryons, made of three quarks (like protons and neutrons), and mesons, made of a quark and an antiquark (like pions). The Large Hadron Collider at CERN is named for the proton beams it accelerates. Quarks come in six flavours — up, down, charm, strange, top, and bottom. They are never found in isolation due to colour confinement; they are always bound inside hadrons. Exotic hadrons like tetraquarks and pentaquarks have been confirmed at the LHC since 2015.