They were first observed by the experiments at the Large Electron–Positron Collider (ALEPH, DELPHI, L3 and OPAL).
The first observation in a hadron collider was made by the scientists of DØ collaboration at Fermilab.
ZZ dibosons are the latest in a series of observations of pairs of gauge bosons (force-carrying particles) by DØ and its sister experiment CDF (also at Tevatron).
Final analysis of the data for this discovery was done by a team of international researchers including scientists of American, Belgian, British, Georgian, Italian, and Russian nationalities.
The ZZ (Z0 + Z0) is the combination which has the lowest predicted likelihood of production in the Standard Model due to the smaller couplings.