CMS Data Express e-Lab Edition


CMS Data Express is a short particle physics masterclass investigation that can be used as part of a workshop or as a short class project. The e-Lab Edition is specifically for use with the CMS e-Lab. Participants examine static displays of a limited number of events. The main goal is to separate Z candidate events other events by visual inspection and then create mass plot for the Z boson.

The Z boson is important in LHC discovery science and as a marker for calibration of LHC detectors: it is a well-known particle, so the location and width of the mass plot give physicists a good idea of how the detector is performing. The Z candidate events are "dimuon" events; the Z can decay into a muon pair. Z candidates are identified by 2 long muon tracks. Participants will search for Z candidates in the data.


Individual or pair:

  • Participate in analysis prep seminar
  • Open the event display file
  • Go to set of events assigned
  • Determine whether each event is a Z candidate (2 distinct muon tracks)
  • If the event is a Z candidate, note the mass, round to nearest odd number, record
  • When finished, count how many instances of each odd number you have recorded


  • Combine numbers of "odd masses" in all groups. (Download xls.)
  • Create a histogram for whole group to observe.


The histogram created by the group is a mass plot. Since the mass of any one type of particle is uncertain by nature and due to experimental uncertainty, it will have a distribution the peak of which is the experimental determination of the mass. Creation of mass plots and other histograms are the central measurements made in the CMS e-Lab but with many more events than used in this exercise.