1. Particle ID Tony Weidberg
Electrons
Muons
Beauty/charm/tau
Pi/K/p
Particle ID Tony Weidberg

2. Particle ID Tony Weidberg
Electrons
See calorimeter lectures
Different lateral and longitudinal shower profiles.
E/p for electrons.
E measured by calorimeter.
P measured by momentum in tracker.
Should peak at 1 for genuine electrons and be > 1 for backgrounds. Why?
Cerenkov & Transition radiation (see Guy Wilkinson’s lectures).
Particle ID Tony Weidberg

3. Particle ID Tony Weidberg
Muons
Use hadron absorber.
Muons only lose energy through ionization  penetrate absorber.
Electrons and hadrons shower  absorbed.
Need > 5 interaction lengths, why ???
Absorber could be hadron calorimeter and/or passive steel.
Muon signature:
Track segment in muon chambers after absorber.
Matching track in tracker before calorimeter.
Particle ID Tony Weidberg

4. Particle ID Tony Weidberg
Muon Backgrounds
Hadron punch trhough.
How can we estimate this?
Pi/K decays
Generates real muons?
How can we reduce this background?
How can we estimate residual background?
Particle ID Tony Weidberg

5. Particle ID Tony Weidberg
Beauty/Charm/Tau
Why is this important?
Detect “long” lifetime with micro-vertex detector
life t~ 1ps  ct ~ 300 mm but remember time dilation can help!
Collider geometry:
Decay happens inside beam pipe.
Measure primary & secondary tracks.
Reconstruct primary & secondary vertices or
Use impact parameter (2D or 3D) wrt primary vertex.
Particle ID Tony Weidberg

6. Particle ID Tony Weidberg
Micro-vertex
Impact parameter resolution
Low pt dominated by multiple scattering.
High pt dominated by measurement error.
Need infinitely thin and infinitely accurate tracking detector.
Best compromise is silicon (pixels, micro-strips or CCDs).
Particle ID Tony Weidberg

7. Particle ID Tony Weidberg
CDF SVX
Silicon microstrips
Wire bonded to hybrid with FE ASICs
Barrel layers built up of many ladders.
Particle ID Tony Weidberg

8. Particle ID Tony Weidberg

9. Transverse flight Path
J/y sample. Plot fight path projected onto transverse plane.
Particle ID Tony Weidberg

10. Particle ID Tony Weidberg
ATLAS Vertexing
Impact parameter resolution improves with pt why?
Why does it saturate at high pt?
Particle ID Tony Weidberg

11. Particle ID Tony Weidberg
ATLAS
Significance = d/s(d)
Compare significance for b jets and u/d jets.
b jets
u jets
Particle ID Tony Weidberg

12. Particle ID Tony Weidberg
Jet Weights
u jets
Combine significance from all tracks in jet.
B jets
Particle ID Tony Weidberg

13. Efficiency b Vs Rejection Power
Plot R (rejection power for u/g/c jets versus eb (b jet efficiency)
Why is c more difficult to reject than u?
Why is g more difficult to reject than u???
Particle ID Tony Weidberg

14. Particle ID Tony Weidberg
Another way to tag b/c
Use semi-leptonic deays:
b c l n Detect charged l in jet at some pt wrt jet axis.
l could be electrons or muons (which do you think would be easier?).
Particle ID Tony Weidberg

15. Particle ID Tony Weidberg
Pi/k/p
Why do we need this?
More difficult…
dE/dx
TOF
Particle ID Tony Weidberg

16. Particle ID Tony Weidberg
Pi/K Separation
Particle ID Tony Weidberg

17. Particle ID Tony Weidberg
TOF L t2 t1
Particle ID Tony Weidberg

18. Particle ID Tony Weidberg
TOF
Scintillation Counter time resolution
Time spread from light paths through scintillator.
Time spread from PMT.
Best resolution s~200 ps.
Spark chambers
Can achieve s~60 ps
Particle ID Tony Weidberg

19. Particle ID by Ionisation
Measure ionisation dE/dx and momentum identify particle type.
Requires very precise measurement of dE/dx  difficult.
Multiple measurements in a wire chamber  truncated mean.
Particle ID Tony Weidberg

20. Ionization: Bethe-Bloch Formula
d=density correction: dielectric properties of medium shield growing range of Lorenz-compacted E-field that would reach more atoms laterally. Without this the stopping power would logarithmically diverge at large projectile velocities. Only relevant at very large bg
BBF as a Function of bg is nearly independent of M of projectile except for nmax and very weak log dependence in d
 if you know p and measure b  get M (particle ID via dE/dx): See slide 21
Nearly independent of medium. Dominant dependence is Z’/A ≈½ for most elements.
Particle ID Tony Weidberg

21. Particle ID Tony Weidberg
12.2 Charged particles in matter (Ionisation and the Bethe-Bloch Formula, variation with bg)
Bethe
Bloch
m+ can
capture e-
Emc = critical energy
defined via:
dE/dxion.=dE/dxBrem.
Broad bg≈3.0(3.5) for Z=100(7)
At minimum, stopping power is nearly independent of particle type and material
Stopping Power at minimum varies from 1.1 to 1.8 MeV g-1 cm2)
Particle is called minimum ionising (MIP) when at minimum
Particle ID Tony Weidberg

22. Ionisation variation with particle type
in drift
chamber
gas
P=mgv=mgbc
variation in dE/dx is useful for particle ID
variation is most pronounced in low energy falling part of curve
if you measured P and dE/dx you can determine the particle mass and thus its “name” e
Particle ID Tony Weidberg