In 1964, two researchers struggling to make sense of hadrons -- subatomic particles affected by the strong force -- individually came up with the idea that they were made up of a constituent particle with three types. George Zweig called them aces; Murray Gell-Mann dubbed them quarks and labelled their three types, or flavors, as "up," "down" and "strange." Physicists would later identify three other quark flavors: "charm," "top" and "bottom."
For many years, physicists divided hadrons into two categories based on the two ways that quarks made them: baryons (including protons and neutrons) were composed of three quarks, whereas mesons (such as pions and kaons) were formed by quark-antiquark pairs [sources: CERN; ODS]. But were these the only possible combinations?
In 2003, researchers in Japan found a strange particle, X(3872), that appeared to be made of a charm quark, an anticharm and at least two other quarks. While exploring the particle's possible existence, researchers found Z(4430), an apparent four-quark particle. The LHC has since discovered evidence for several such particles, which break -- or at least substantially bend -- the established model for quark arrangements. Such Z particles are fleeting, but may have thrived for a microsecond or so following the Big Bang [sources: O'Luanaigh; Diep; Grant].