Tiny URL for this page: http://tinyurl.com/atlasde0.
Introduction
ATLAS Data Express is a short particle physics masterclass investigation that can be used as part of a workshop or as a short class project. 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 we will study are "dimuon" events; the Z can decay into a muon-antimuon pair. Z candidates are identified by 2 long muon tracks; each will appear as a combination of a short blue track in the inner detector (inner black ring) and a longer orange track in the outer muon chambers (blue rings). Participants will search for Z candidates in the data.
Instructions
Individual or pair:
- Participate in analysis prep seminar (slides) (ATLAS animation)
- Open the event display file
- Go to set of events assigned
- Categorize and record each event as
- Z → μ+μ- candidate (2 distinct muon tracks),
- background (anything else).
- For each Z candidate, note and record
- the mass, rounded to nearest odd number (found at upper right of event)
- whether it is an electron or a muon event.
- When finished, count how many instances of each odd number you have recorded.
Group:
Use your own resources to
- Combine numbers of "odd masses" in all groups.
- Create a histogram for whole group to observe.
- Analyze other aspects of the data (optional).
Help: Use the Google spreadsheet.
Discussion
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.