CMS J/Ψ Measurement
This page uses the "old" iSpy-online. For iSpy-webgl, please refer to
CMS Masterclass Documentation.
You will study decays containing muon pairs to determine which events are J/Ψ (charm-anticharm meson) candidates and then create a histogram of the mass calculations for the events that pass the "student trigger."
When a J/Ψ particle decays, it typically produces a pair of muons. Look CAREFULLY at the two events below. Is there evidence of muon pairs (red tracks) in either or both events? Could either be a candidate for J/Ψ? Is the evidence weak or strong? Are you confident of your conclusions?
Test 1: Opposite charges
To be a possible J/Ψ candidate, the event must have two muon tracks of opposite electric charge.
If the event does not pass the charge test, the event almost certainly is something other than a J/Ψ decay: rate it "0" (see below).
If two muons pass the "charge test," then rate the likelihood of a J/Ψ candidate by rating each muon track. If there are more than two, rate the two best of opposite charge.
Elements of a J/Ψ Candidate Event
Before You Start
If you are not familiar with iSpy Online:
Rate the J/Ψ Candidates
Use the guidelines above to rate the candidate events. Apply what you learned as consistently and rigorously as you can. The rating of the J/Ψ candidate on a 0-3 scale is based on your study of the muons in the event display:
0 - NO CHANCE
1 - POOR
2 - FAIR
3 - GOOD
Enter the rating for each event in the Data Spreadsheet. Mass calculation—the second part of the masterclass exercise—is enabled in the spreadsheet only when a muon ratings are given.
In cases of anomalous or difficult-to-rate events, consult with other students, teachers, and mentors to apply as consistent a rating as possible.
General Consistency Check
Count up how many events of each rating you have in your set. Compare this with other groups. If the numbers are very different, discuss your criteria and see if someone needs to make an adjustment.
If you finish all 100 events, start a new set, preferably one that no one has done. There are 2000 events and the more you can work through, the better your overall results will be.
The whole group does this part of the CMS Masterclass under the leadership of the mentor.