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Study the W bosons produced in the Large Hadron Collider.
Tiny URL for this page: http://tinyurl.com/lnwmrf8 |
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Introduction
Protons collide with incredible energy in the Large Hadron Collider. Sometimes the result of one of these collisions is a W boson - the particle which mediates the weak nuclear interaction. W bosons can be positive (+) or negative (-) in charge. But...
- How often are W+ bosons made compared to W- bosons in the the LHC?
- Should it be equal because nature has no preference?
- Should we see all W+ because the proton is positive?
- Can we find out?
Let's try.
Procedure
- Learn a little about LHC, the CMS detector, and finding W candidate events. Look at the introductory slides.
- Make teams of two and divide the available CMS events among the teams. Each team also gets a report page.
- Characterize your events and count them:
- W+ candidates have a single long red muon track which curves clockwise in the magnetic field of CMS.
- W- candidates have a single long red muon track which curves anti-clockwise in the magnetic field of CMS.
- W? events are too hard to measure so we cannot tell if they are W+ or W-.
- Background events have more than one muon or are altogether different.
- Add them up on the report page. Then collect all the reports from all the teams and add up the number of W+ candidates and the number of W- candidates. Calculate W+/W-. If you like, you can use this spreadsheet.
- Find what the result was for CMS. How close was your group? Why do you think we get the answer we get? (Hint: it has to do with the structure of the proton,)
Next steps
- Did you notice the mass in GeV on each event? We use these to find the mass of the Z boson in the standard CMS Data Express. Try it with your students!
- Your students can do even more with a CMS or ATLAS masterclass. Talk with a physicist near you about International Masterclasses.
- For a more intense data experience, try the CMS e-Lab.
- Have questions about this activity? Send an e-mail and ask.