Part 4 of the challenge is a little bit more difficult. Events of the types you met in Parts 2 and 3 will be mixed up together. We won't tell you in advance which is which. So, first you have to decide whether the event you're looking at is the type in which a particle-antiparticle pair has been produced (like Challenge Part 2) or it is the type of event in which a \(W^{+}W^{-}\) pair has been produced (like Challenge Part 3). After you've done that then see if you can identify exactly which sort of event you're looking at!