Symmetry: In 2008 the Belle experiment in Japan found the first strong evidence of a particle made up of four quarks. All the previously discovered composite particles—mesons such as pions, and baryons such as protons—have comprised either two or three quarks. Now Fermilab's DZero, which has been analyzing data collected from the Tevatron, has confirmed the discovery of a tetraquark particle, hints of which were first seen in July 2015. And it differs from all previous tetraquark candidates because the four quarks are different flavors—up, down, strange, and bottom. The continued discovery of new tetraquarks and last year's discovery of a pentaquark at the Large Hadron Collider are helping theorists develop a better understanding of how quarks behave.
