1. Experimental Particle Physics PHYS6011 Putting it all together Lecture 4
6th May 2009
Fergus Wilson, RAL

2. Collider Experiments Top production Higgs Production So far:
Accelerators and colliders
Particle interactions
Types of detectors
Combine them to do physics…
Example: CDF at the Tevatron
Proton-antiproton collisions
Fermilab and the Tevatron
CDF and DØ
Identifying particles
Identifying physics processes
Top production
Higgs Production
6th May 2009
Fergus Wilson, RAL

3. Reconstructing Collisions
What happened here? e+ e- ? q _ e+ e- Z
or something more exotic.....
extract maximum information from outgoing particles
6th May 2009
Fergus Wilson, RAL

4. Proton-Antiproton Collisions
Protons are composite objects: valence & sea quarks; gluons
Really parton-parton collisions
Underlying event:
Most lost at low angles
Some in detector
pz unknown
Extra detector hits
Initial partons unknown
Huge total cross section (10s of mb)
Hard scatter
Underlying event
1 mb = cm2
6th May 2009
Fergus Wilson, RAL

5. Cross-Sections pb e+e- GeV mb γp GeV mb mb 6th May 2009
1 mb = cm2
1 fb = cm2 pb
e+e-
GeV mb mb mb γp pp γγ
GeV
6th May 2009
Fergus Wilson, RAL

6. Fermilab Major discoveries 30 miles west of Chicago 10 square miles
Started operating in 1972
Major discoveries
1977 Bottom quark
1995 Top quark
1999 Direct CP Violation
2000 Tau Neutrino
2006 Bs Oscillation
2009 Higgs Exclusion Limits
6th May 2009
Fergus Wilson, RAL

7. Fermilab Accelerators
Collider
Experiments
Fixed target beams
6th May 2009
Fergus Wilson, RAL

8. The Tevatron Run II Upgraded for 2001 s = 1.96 TeV
proton-antiproton collisions
36 bunches
396 ns bunch crossing
L ~ 1032 cm-2s-1
3 interactions per crossing
6.5 fb-1 by 2009
6th May 2009
Fergus Wilson, RAL

9. The Experiments DØ - optimised for calorimetry
CDF - optimised for tracking
6th May 2009
Fergus Wilson, RAL

10. CDF 2001Upgrade Higher luminosity Newer technology 6th May 2009
Fergus Wilson, RAL

11. (drift and scintillator)
CDF Components
Muon detectors
(drift and scintillator)
TIME OF FLIGHT
L00
Iron/scintillator
Lead/scintillator
1.4 T B Field
Very fast scintillator
Fast drift chamber
8 layers of silicon
6th May 2009
Fergus Wilson, RAL

12. Trigger and DAQ A million channels at 2.5 MHz DAQ Data AcQuisition
42*132ns=5544ns
DAQ
Data AcQuisition
Processing
Storage
Keywords:
Pipeline
Latency
Buffer
Trigger Rate
Trigger Inputs:
Number of tracks
Energy Clusters
Particle Type
200 kB at 100 Hz
6th May 2009
Fergus Wilson, RAL

13. Feynman Level Directly observe X and Y if: If not:
Hard process with final state X and Y
Directly observe X and Y if:
If not:
Long-lived (>picosecond)
Reconstruct from decay products
Interact with detectors
Reconstructed from “missing” transverse momentum pT
Not confined (e.g. not a quark)
Produce jets
6th May 2009
Fergus Wilson, RAL

14. Standard Model Particles
Lifetime ~ ps
Confined
Short lived
Non interacting
6th May 2009
Fergus Wilson, RAL

15. Particles Signatures Electron, photons, muons and jets π±, K ±, p
Tau lepton ID depends on decay mode
6th May 2009
Fergus Wilson, RAL

16. Vertex Tagging
b decay vertex
c decay vertex e+ e-
primary vertex
b-quark, c-quark, τ-lepton will travel a few mm then decay
Precise tracking shows “displaced vertices”
Easiest for b hadrons
6th May 2009
Fergus Wilson, RAL

17. Signatures: Two Electron Event
Small hadronic energy
Large EM energy
High momentum track
Tracks and energies below a threshold not shown!
6th May 2009
Fergus Wilson, RAL

18. Signatures: Dijet + Missing Energy Trigger
Two jets
energy in EM and hadron
many tracks
Alternate view of calorimeter
pT not balanced
undetected particles
6th May 2009
Fergus Wilson, RAL

19. Finding Top Quarks Top quark discovered at CDF and DØ in 1995
Need to identify top pair production:
Br (t→bW+)  100%
Br (W→qq)  70%
Br (W→lν)  10% per lepton
Semileptonic channel
l- is electron or muon
l- easy to identify
only one neutrino
q is a “light jet” from a u,d,s quark.
NB may be higher order effects
6th May 2009
Fergus Wilson, RAL

20. Top Pair Production Electron or muon 20% of the time Signature:
2 light quark jets
2 bottom jets
One electron or muon
Missing transverse momentum (because of the neutrino)
Extras:
Underlying event
Higher order processes
Multiple interactions
6th May 2009
Fergus Wilson, RAL

21. Top Event Muon Light quark jets 3 cm Missing pT b tagged jets
6th May 2009
Fergus Wilson, RAL

22. Finding the Higgs and writing your first paper
Next Time...
Finding the Higgs and writing your first paper
6th May 2009
Fergus Wilson, RAL