1. Masterclass 2010 Students exploring the Universe from the inside out.

2. The edge of physics right now.
Physicists are just starting to take data from the Large Hadron Collider (LHC), the largest and most powerful particle accelerator ever built. ATLAS and CMS, the giant detectors for LHC, sit in caverns deep below countryside near Geneva, Switzerland, poised to make discoveries about the basic nature of the universe. To do that, we first have to make sense of the data that these detectors produce.
That’s where you come in.
Do not read…paraphrase. Let the students read. You may point out that the image is of the LHC.

3. Background: Experimental Particle Physics in a Nutshell
Rutherford’s Gold Foil Experiment ( )
Ask what students know about the Rutherford experiment. Then redirect toward the idea of the “prototypical particle physics experiment”.
Ernest Rutherford
( )
Fired beam of positively-charged alpha particles at very thin gold foil.
Alpha particles caused flashes of light when they hit the zinc sulfide screen
Result: discovery of the atomic nucleus

4. Rutherford’s Work Set the stage for all particle physics research
Explain how these features are seen in particle physics experiments today. Point out that we use particles other than alpha.
You will take the places of Geiger and Marsden in a more modern experiment.

5. FYI: LHC and LEP are colliders
Take Rutherford’s original experiment and double it…
Now soup up the beams and make them the targets for each other; add a cylindrical detector to catch what comes out…
Ask students: “Why a cylindrical detector?”

6. Final form
Ask students: “Why rings? Why not straight line accelerators?”
First LEP, and now LHC, are buried ~100 m below the surface near the Swiss-French border

7. How to Build a Working Detector
The challenge
Measure particle properties without interfering (too much) with other particles.
Electrons & hadrons interact very differently.
A detector which measures electrons efficiently won't do a very good job on hadrons. And vice-versa.
Measure electrons without destroying your ability to measure hadrons.
The solution
A set of detectors each of which measures one thing and doesn't prevent later measurements.
Recall the question of a cylindrical detector. Does this shed more light on the reason to use this configuration?

8. How to Build a Working Detector
Generic Design
Concentric cylinders wrapped around the beampipe
From inner to outer....
Tracking – measure particle trajectories
Magnet – bend path for momentum measurement
Electromagnetic calorimeter – measure energy of e/γ
Hadronic calorimeter – measure energy of quark jets
Muon chamber – measure muon momentum & trajectory.
Point out features. (Note to teacher and students: The magnet placement will vary, depending on the design of the particular detector.) Then…

9. Transverse Slice Through CMS
…point out the same features in CMS. After showing animations, press ESC to exit.

10. What can we learn from this event display?
Circular tracks?
Yellow sprays?
What carries the most momentum and energy?
Is there a balance…and what would it mean?
Where do all the tracks come from…and why?
Optional slide…the point is to introduce an LHC event.

11. Assignment: Masterclass
In this Masterclass, you will work with physicists, teachers, and fellow students to analyze data actual experimental data from CERN. You will study events from the Large Electron-Positron (LEP) collider to investigate how the Z-boson decays.
Why? We need to understand the Z-boson to:
Understand LHC detectors: Z decays are basic background and the first thing we will measure.
Search for Higgs through the H Z0Z0 channel
Do not read…paraphrase.
Help us get the LHC detectors ready for data!

12. DELPHI at LEP: Our Z Lab Data Collection 1989 – 1999
e+e- collider: “clean” and “tuned” events  scientists can tune the beam so all the energy can go into a single particle
45.5 GeV GeV  91 GeV (Z mass)
Intensive studies of Z- and W-bosons
The conclusion of this slide, on which you should not spend too much time anyway, is a good break point to go to the DELPHI animation at

13. Particle Identification
You are working with Z0 particles.
Mass = 91 GeV.
Remember charge and momentum conservation!
Z decay modes are:
Z0  e+e-
Z0  μ+μ-
Z0  τ+τ-
Z0  2q
Z0  3q
Z0  4q
Explain decays in words (e.g. a Z-boson decays into an electron and a positron) and that Z  2q etc means Z-boson decays to 2 jets of hadrons etc.

14. Particle Event Display
Hadron Calorimeter – this section measures the total energy of the hadrons
Ecms – Particle energy measured before collision (91 GeV)
Tracking Chamber — determines charged particle trajectories
Nr tracks– Number of particle tracks measured by detector after collision (20 tracks)
Muon Chamber – this section detects the presence of muons (shown as + signs)
Step-by-step.
Electromagnetic Calorimeter – this section measures the total energy of the e+, e-, and photons created
Energy– Total particle energy measured after collision (70.6 GeV)

15. Decay Signatures Z0 → μ+μ- Nice clean single track events.
Energy/momentum of lepton pair is ~Z mass.
Leaves some energy in Ecal and/or Hcal (rectangles)
Remind students of cosmic rays if they are familiar. Ask students what each bullet means. (Muon on the right.)

16. Find the best muon candidates
Don’t simply go to the “right” answer: engage discussion. Explain why we say “candidates”. (Best muon candidates: A and C.)

17. More decays
Z0 → e+e-
Nice clean single track events, back-to-back, just like muons.
Energy/momentum of lepton pair is ~Z mass.
Large Ecal energy deposits
No + signs in muon chamber.
Ask about meaning of each bullet. (Electron on the left.)
Which is the better Z e+e- candidate?

18. Which is the best e+e- candidate?
Engage discussion. (Best electron candidate: D.) Ask them if there is anything else familiar. (Muon candidate, B.)
What about the other events?

19. Decay Signatures Z0 → νν This is the tricky one!
τ → e or μ or quark jets
Big drop in energy (due to ντ’s).
τ → leptons + neutrinos
τ → hadrons + neutrinos
τ → 3 hadron tracks
τ → 1 hadron track
1 or 3 tracks per τ particle
Tau event example: Large energy loss (presence of neutrinos); one electron and one muon detected (small number of tracks).
Explain this in detail. Important: (A) taus each decay into product plus neutrinos, (B) we do not see taus because of short lifetime, (C) detector does not see or measure neutrinos – hence missing energy (usually > 60 GeV loss), (D) generally 2, 4, or 6 total tracks.

20. Where are the tau candidates?B. D.
Discuss a lot. Why can we eliminate A? Discuss why B is tempting but best to eliminate (energy too high, too many tracks). C could be
Z  taus  electron and muon. D could be Z  taus  quarks. Note energy losses. Ask a lot of questions. Warn students about “too many taus”.
Beware of tau-wannabes!

21. Decay Signatures
Z0 → quarks hadronic jets (2 jets, 3 jets & 4 jets)(\
A jet is a spray of particles that results when the energetic separation of quarks makes more quarks...and more...
Many tracks
Lots of energy in Hcal.
Possible hits in Ecal or muon chamber.
Jets can also produce leptons.
Discuss Z  qq, quark “confinement”, and how quarks pulling apart creates sprays of particles from energy in strong interaction. Remind them of mass-energy equivalence. For Z  neutrinos, remind them of what we said before about detector unable to “see” neutrinos.
Z0 → νν
No signature in the detector!
Can’t see it; don’t know it’s there.
What do you do? Nothing (for now).

22. How many quark jets in each?
A has 2. B has…zero (trick question – it is a muon candidate). C has 3. D has 4. Explain about color-coding of jets by software.

23. 2-jet, 3-jet, yellow jet, blue jet So what? (Advanced topic!)
Well, look at how hadronic jets are formed from quarks and the energy of the strong nuclear force.
The next 3 slides are an option for discussion of alpha-s. Gauge your audience and either proceed or skip. If you skip, still have them record numbers of jets; we can then introduce alpha-s as a parameter to check when sending in the data.

24. Sometimes, though, one quark emits a gluon. (What’s that?)
The Z-decay starts as before.
This time, one of the quarks emits a gluon. (Why?) All three particles have strong potential energy between them…
…which hadronizes into 3 jets.
Optional (see comments, slide 23).

25. Making gluons makes the strong force
So the strong coupling constant, a measure of the strength of the
strong force, depends on the probability of quarks emitting gluons.
This can be determined for Z-bosons as the ratio of the number of
3-jet to
2-jet
events
Optional (see comments, slide 23).
We’ll check this in LEP data to help calibrate our results for LHC!

26. Go forth and analyze… Next steps: Practice Talk with physicists
Make teams of two
All the teams together analyze 1000 LEP events
Report! Rapport! Rejoice! Relax!
The data awaits you!
Follow with (A) intro to event posters and (B) going through about events together from Hands-on-CERN. (Show features.)