Do it!

You will use your new knowledge of identifying particles and some basic physics and realize that you have just mastered a powerful tool to also "discover" new particles never seen in Nature before, such as the Z', a hypothetical big brother of the Z boson. If you don’t know what a histogram is, follow this link. We will use HYPATIA’s invariant mass calculator. To see how to use it, follow this link to the HYPATIA official website. You will use these tools together with the particle identification information from HYPATIA in this exercise.

Your collision images (event-displays) contain a mixture of events with

  • Z-boson (and other particles) into electron-positron or muon-antimuon,
  • Higgs candidate into photon-photon,
  • Higgs candidate into 4-leptons,

but also completely different types of collision products – we referred to as background events, such as jets stemming from quarks or gluons and W bosons. (If you don't remember how these look like, go back to Identifying events). You should use your knowledge about particle identification and the HYPATHIA invariant mass calculator to investigate whether a Z boson was created or not.

What to do

  1. In HYPATIA, for each collision, try to find signs of the existence of particles such as
    • a Z boson, by hunting for an electron-positron pair or a muon-antimuon pair,
    • a Higgs boson by hunting for a photon-photon pair
    • a Higgs boson by hunting for 2 lepton-pairs (e+e-e+e-, e+e-μ+μ-, μ+μ-μ+μ-)
    If you cannot find such particle pairs, the event might be a background event. Use the pointing tools and particle information in HYPATIA to make your decision. To help you keep track of which events you have looked at, fill in the tally sheet.
  2. If you believe you see the decay-products of one of the particles above, pick the corresponding tracks or objects and insert them into the HYPATIA invariant mass table.
    1. If you find a pair of electron- or a pair of muon-tracks you might have found a Z boson or the much lighter J/Psi or Upsilon particle.
    2. If you are lucky to see 2 pairs of leptons, insert them both; you may have a Higgs candidate decaying to 4 leptons!
    3. If you believe you see a candidate Higgs boson decaying to a pair of photons, pick both photons and insert them into the HYPATIA invariant mass table.
  3. If you believe the collision resulted in a background event (no pair of leptons with opposite electric charges and nor pairs of photons), ignore the event and proceed to the next one.
  4. After analyzing all events, Export the Invariant Mass Table from HYPATIA: File-> Export Invariant Masses. The file is called Invariant_Masses.txt by default (do not change it). Place the file on your Desktop so you can easily find it.
  5. Go to the plot submission page, and upload the invariant mass file you just made.