The DZero collaboration searched for signs for ZZ production in nearly 200 trillion proton-antiproton collisions delivered by the Tevatron. In one analysis, scientists looked for Z bosons decaying into pairs of electrons or muons. Just three events were observed in this mode. But the signature is remarkably distinctive: the predicted background is only two tenths of one event (see graph). (Note: Electrons and muons belong to a class of particles known as leptons.)