The discovery of ZZ production (red check mark) is an essential prelude to finding or excluding the Higgs boson at the Tevatron particle collider at DOE’s Fermi National Accelerator Laboratory. The discovery is the latest in a series of observations of so-called gauge bosons, or force-carrying particles, by DZero and its sister Tevatron experiment, CDF. The series began (from left) with the study of collisions that produced a single W or Z boson and the already rare production of a W boson plus photon; then Z boson plus photon. In the last couple of years, Tevatron experiments discovered the even rarer production of W pairs, then WZ. Now, DZero has discovered the ZZ production. The ZZ process is the final step before reaching the even rarer process of a Higgs boson decaying into a pair of W bosons.