This is similar to the quark - antiquark event, except that a gluon (a particle which carries the strong nuclear force and holds the quarks together in the nucleus) is also produced, and gives rise to a third jet when it decays. Again, there is a secondary vertex visible - perhaps from a b or c-quark decay, indicating that the gluon jet is probably one of the other two. Gluon radiation, as seen in this event, is analogous to photon radiation, which can be seen in a later event. The gluon is the force-carrier for the strong force, just as the photon is the force-carrier for the electromagnetic force.

Notes for experts: This is a classic "Mercedes" event. The red jet has a secondary vertex 0.8 mm (3D) from the primary vertex. The jet energies are all approximately the same, 30 GeV.