"Four Fermion" Events

Remember the example diagram we used to represent events:

Instead of flying out and being observed in the calorimeter, sometimes the photon produces an additional particle-antiparticle pair. Such events contain two particle-antiparticle pairs. For example:

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These events go by the jargon name "four fermion" events. Here is an example event that contains electron-positron and muon-antimuon pairs:

Example "Four Fermion" Event