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 observations began with the study of the already-rare production of W bosons plus photons (W + γ); then Z bosons plus photons (Z + γ); then observation of W pairs (W + W); then a mix of W and Z boson (W + Z). The ZZ (Z + Z) is the combination which has the lowest predicted likelihood of production in the Standard Model due to the smaller couplings.