Hypatia Event Display - Identify Z boson decays

A brief tutorial on how to use the online ATLAS event display Hypatia for a Z boson decay exercise.

In this exercise the students need to identify which of the 50 real events that have been recorded by the ATLAS experiment at CERN contain Z boson decays. The rest of the events are called background and they can be W boson decays, cosmic rays or any number of other processes.

Z bosons can decay in a number of ways, but in this exercise we will only look at Z to lepton-lepton decays. The students have to select the pair of lepton tracks that are created by this decay and insert them into the Invariant Mass table. This calculates the invariant mass of the particle that produced them (which if they have selected the right tracks would be a Z boson with a mass of 91,2 GeV).

After going through all the events and inserting the proper tracks from each of the decays, the students can look at the histogram of invariant masses (Mll) which gives them the mass and width of the Z boson.